Do you really think a public roadmap would make any difference? Imo, it seems like there's still a general awareness problem.
I for one very extremely much believe so.
When people are sniffing around something new that's one of the very first things they look to. If it isn't there then many a time they're not going to burrow any further. There are bog standard things you look at before going further with most projects - website, market position, Bitcointalk mentions, and a roadmap is very much in there too.
It may seem simplistic to someone heavily involved, but people start off on a simple basis anyway and then the details draw them in later on. And I wouldn't really class it as marketing. It's a basic courtesy in the minds of many - you're here in our present, here's a few bullet points about where we're planning to take you, or where you may take us.
It reminds me a little of what that Cache bloke was saying. He had to dig pretty hard on the website to find the info that excited him. It wasn't immediately in his face.
It's not as if it's a mind scrambling task either. It's a few hours of work which may pay off adoption wise more than tens or hundreds or thousands of hours of effort elsewhere. I'd happily do it myself if I had a clue about anything.
For something so simple and so ubiquitous elsewhere I find it mysterious that it doesn't exist though I recall mentions of something being put together on Telegram. Once it's in place it may only need a few minutes of maintenance per month but it would make a big difference.
It's one of the absolute smallest outlays of effort vs potential onboarding return.