What role should a product launch have with your existing customers?

Existing customers are the best source for new product adoption and should be the primary target audience. With new customers, you need them to buy into your company, and then buy into your new product. That's hoping for two miracles, vs. one with existing customers. 

Plus, it's so much easier to get your new product info to existing customers. You know who they are and conceivably, you have a standard way of contacting your existing customers. 

I'd suggest paying extra attention to in-product messaging about new products and features. Emails, social, PR are very important... but your customer has to be paying attention. Events are captive, but your customer has to come to the event. Your best chance of conveying new product info is inside your product - say when folks log in or use a related product/feature. You'll get the captive attention many more customers. 

First of all, sometimes product launches are about existing customers. Maybe you're launching something meant to dramatically improve their experience, or help them expand their engagement with the product. In those cases, they are your primary audience and all of your comms should be shaped to inform them and motivate them to take the action that you want them to take. 

However, let's say that your launch is about attracting new users. You still want to engage your existing users as evangelists, influencers, storytellers, and examples. Nothing is more powerful than someone who already uses your product telling new people how it's transformed their lives for the better. You want to make it very easy for them to do this and build them a platform for their voice to be heard. Supply them with all the information they need to share your news to their followers on social media, showcase how they've been succeeding with your product in customer stories that you post to your website, YouTube channel, etc. Make sure your launch is embroidered with all kinds of examples of existing users' experiences. What they've done with your product. The value they've realized. Your happiest existing customers are going to want to support your success. Make them feel even more appreciated by aligning your interests with theirs, cross-promoting their brands or products, etc. at the same time as you show your audience how your product has helped them. 

You should never be launching a product just for the sake of launching it. Clearly define the objectives of the launch and commit to a primary and secondary. The role your cusotmers play will clearly follow out of the objectives and answering your question becomes easy.

If increased retention/decreased churn is an objective, plan around that. If this is a new product and up/cross-sell is an objective, plan around that. If this is a set of new features to an existing product, plan around that. 

Existing customers should be primary audience in any new product launch plan

1. They are familiar with your company, your products. They have literally invested time and money to be familiar with your solutions. They are likely to be the earliest adopters of your new products due to this familiarity of contracting, relationships, UI/UX,use cases, and more

2. Even if your new product is for a distinct buyer/use case/user than your existing users , you are likely to find them in existing customers. Call it ease of contracting, familiarity with CSM, or trust for a peer recommended tool - there are so many reasons why finding new users in existing customers is easier than cold hunting in a new account 

3. Existing customers are also most likely to provide social proof/customer stories/quotes/validation/ROI proof points etc. 

4. Existing customers are also the primary audience to be invited to a launch event. Launch updates/newsletters go to them. Early adopter/limited preview sign-ups come from them. Event invites sent to them. Post launch trainigs are for them. We literally design most of our launches with existing customers in mind

With Prospects/non customers - we focus not just on the 'new launch' but on the entirety of our offerings. I often see PMM teams take an amazing new innovation to prospects as the shiny new object, while ignoring the product that is already there. Prospects need to hear your entire story - the before->after state you are promising them, the what/why/how of your product/platform - not just your shiny new launch.

Existing customers should be your product champions. You should be getting them involved in betas, cusotmer advisory panels and the like.  They can help shape product direction and help you understand messaging that will resonate in the market.

Depends. If you have a risk averse target market and you need reference customers as proof, customers are very import. Identify potential candidates for your new product within your customer base and work like hell to turn them into references (I don't care how, just get them to sing like a bird). 

If your new product is targeted at your customer base, get them onboard early like Nina suggests. 

In short, yes the product launch should play a role with your existing customers. As Mike wisely pointed it, the nature of the role should be determined by the objectives of the business.

I use a communication matrix to define the desired outcomes and appropriate tactics, channels, and messages for each audience segment (customer, prospect, target market, etc...).

In principle, you want customers to become ambassors. So neglecting them from a launch plan would be short-sighted in most cases.

Customers MUST be a part of any product launch. 

While you never want to treat them as "guinea pigs" for any new feature, they are your best resource to test the market fit before you even dream of actually pushing any update to product and promoting it. Including your customers in the launch is vital. Keep the lines of communication open during any product launch.

Any product launch has a growth component in it - be it for new logos, new revenue lines, or even expansion of current contracts. Your current customers are a growth lever that most orgs neglect.

When looking at a product launch, while assessing potential opportunity/pipeline creation, any marketing team must also look at the impact it will have on existing customers - be it from a revenue, adoption, or retention standpoint.

In addition, as you prepare to bring a product to market, you will need proof points to give social credibility to the value you claim to give. It's easy to get testimonials, ROI statements, and even case studies that will bolster your launch's success.

I believe that this question has a two-fold answer. The first being that existing customers should play a large role in product launches. Since they have already bought into the previous models, you want them to remain loyal with new features. Launching something new without considering them in mind could have a hugely adverse effect. Also, as David mentioned above, the refrences from existing products is what will help drive success for the launch and the overall lifespan of the product. 

On the other hand, growth is the name of the game, so there obviously should be an element of focus towards new customers. New product ambassadors are critical in spreading the message, just as the base of customers are essential for establishing the reputation of the product.