At what stage of a company should a product marketing team think about resourcing an industry-first approach?

This one all depends on the product, market, and customers. If you're an industry-specific solution and just getting started in market, taking an industry bent first will help you differentiate against the horizontal plays. Being able to tell a credible "insider story" and keep the team focused on material problems is a huge advantage. 

Alternatively, if you have a horizontal play that's starting to get real traction in more than 2-3 industries (and by traction, I'd say if you have 3 industries driving more than 50% of your sales, it's time to focus). You'll need that industry credibility and POV to move beyond the early adopters and start honing the product roadmap.

Also, by this time, the complexity of the product and the sales motion will be more than enough to occupy a horizontally-focused PMM team. Diversification can accelerate focus; leverage that. 

Every single company, starting on the very first day that the founders have an idea on a napkin, should think, and resource, industry-first. Surprising? Well, that's because early stage startups need to have an extremely narrow focus on their ideal customer, which tends to be within a single industry at first.

After that, and at scale, it can really depend on the type of product you're marketing, and how different the value propositions are by industry. At Procore, we've found that our core solutions are an amazing fit for anyone in the broader construction industry, but the way we the solutions are used -- the cooresponding messaging -- differs enough that we needed to segment out first by General Contractors (our initial audience), then by Specialty Contractors, then project Owners, in order to have success in the sales cycle.

Once your team realizes they have (1) captured a substantial part of the initial launch industry, and (2) the "core" messaging won't be successful in other industries for whatever reason -- it's time to specialize. 

The focus should always be on the needs and wants of the customer. Storytelling needs to be at the center and strategy should be based on customer problems and marketing should align to the solution. 

Industry based marketing should be a priority once product market fit has been established across an intiial target market. Targeting subsets of customers by vertical and segment is key in order to align value based messaging with customer pain. Creating seperate marketing strategies allows for accelerated growth instead of a one message approach across industries that falls flat. Once you start segmenting based on needs and preferences, is when the fun starts and the true growth happens. This requires extensive customer research - truly understanding what they care about most, and then aligning the messaging and marketing to the correct channel. 

Once there's not only product market fit (which almost all companies prematurely declare victory around - sorry but it's totally true) but also determination and commitment that a given industry or industies are the decided way to GTM. If products are horizontal and sales teams are horizontal then having just the marketers aligned vertically spells trouble. An industry-first approach has to be resourced beyond marketing, dabbling's not going to get anyone anywhere.  

There are a couple dimensions to this that I find helpful to double-click into depending on your company's situation. First is creating a clear delineation between Industry Marketing and Industry Product Marketing. 

To me, the initial need for Industry Marketing is driving awareness and brand relevance within a specific industry. This is done through speaking the native language of that industry with relevant content marketing, primary research into an industry’s end consumers, internal research into industry buyer personas, building up internal and external influencer marketing programs for SMEs and orchestrating their point of view thought leadership which is used to influence vertical analysts, media, and the industry’s professional community. It also means industry-specific demand generation programs that invest in media buys, and 3rd party events with relevant industry trade associations and publications, and an industry-relevant customer marketing program that demonstrates the success (business outcomes) your solutions deliver to influence a successful customer’s peer group.  

For one tangible datapoint, Salesforce chose to kick-start industry marketing in 2014 with a few FTEs and I was fortunate to join the team at that time. *Note, this was 1 year before we had investment to build industry-specific products. 

When the day comes that your CPO puts purpose-built industry product(s) on the roadmap, then you’ll want to staff up an Industry Product Marketing team in advance of GA (I recommend at least 9 months) to support the advanced message testing, positioning, go-to-market, launch planning, channel readiness, and post-GA evolution of those new industry product(s). The Pragmatic Institute’s annual survey collects industry benchmarks for team ratios. The most recent survey shows that for every two product managers dedicated to an industry product, you’ll need 1 dedicated industry product marketer. https://www.pragmaticinstitute.com/