What kind of PMM organizational structure is ideal for ensuring that PMMs are set up for success (in this case, to influence the Product roadmap)?

I've seen product marketing fall either under Marketing or Product with dotted lines to specific businesses they support. There are pros and cons to either structures but generally, aligning under the product org will allow you to be more tightly aligned and have greater influence on the product roadmap.  

Recently, the way my PMM teams have been structured has been Inbound (or Core, Stream, etc) and Outbound (GTM). This type of team structure divides up PMM teams with those that 

1) Work closely with GTM - sales plays, customer advisory boards, ABM camapign and

2) Those that work closely with Product, Engineering and UX design - Product roadmap, launch preperation, sales enablement, demos, etc. 

I find this to be the most ideal when being asked to influence product roadmap is a core part of your job. However, this does take away from your ability to influence MQLs, as your role becomes much more technical, and less around structuring how sales and marketing align together. I've done both, and it really depends on what you enjoy doing. I also ask my own team what they enjoy, and try and make sure they work closer in areas that they feel they can make the most impact. 

If your main goal is to stay tightly aligned with PM, then its best to mirror their structure as much as possible. E.g. in my world we have alignment at both the product VP/GM level down to the individual PM level. Its not necessary to have a 1:1 between PM and PMM because that can be inefficient. Said another way:

1. Product VP/GM <--> PMM VP. Alignment of portfolio/solution level messaging, big pricing or GTM decisions, influencing longer term product strategy

2. Product leader <--> PMM leader. This can be many-to-1. Goals more short-medium term, including release marketing, competitive intel, sales/customer feedback, etc.

As it relates to influencing roadmap, breadth is important. If youre spread too thin (I don't mean PM:PMM ratio, I mean commonality in what you cover--more on this later) then you wont be able to go upstream and influence roadmap because you'll be playing defense all day. 

I personally think being tagged to a vertical or a persona will make it harder to influence roadmap because you'll be seen as a person that executes a launch to a segment; rather than being a person that understands both the product and the user to think like a PM. Nuance here: Insights around a persona or vertical will help, but structure matters, because you want your internal teams to think of you as mapped to their product bringing persona insights; rather than mapped to a persona trying to connect to products. 

So as it relates to being spread too thin--can you find a common denominator in terms of what you cover, and can you bring insights back to your 3+ PMs about that commonality? I focus on Google Assistant and 1p/3p apps. So thats a lot of PMs on Assistant, PMs on 1p app teams and BD folks on 3p app teams; so the commonality is the extensibility of Assistant. The insights are around what makes app usage sticky and what Assistant can bring to an external app. If my ratio was lower, but my focus was on disconnected topics, I wouldnt be able to pull together a common thread to bring back insights that would help PMs, unless I prioritized one product over another.