One of the main reasons that made Powerplay a game mechanic not as widespread as fdev hoped for, it's the infamous merit decay: basically you were forced to keep playing the game to keep your bonuses and privileges, that was especially a problem for people that had limited time to play for real life reasons.Given Galnet having regular updates and various other places it is mentioned in game awareness is probably fairly high, how many of those do more than try and collect modules is the more important question.
So I would guess 60% aware of it, 15% of them do more than collect modules.
New Powerplay will grant access to all the modules AND the different Powers' bonuses basically forever once you've reached the appropriated rank, then the weekly rewards in the fashion of Community Goals should be a good incentive to at least stay pledged.
We'll see of course, people will be free to pledge a particular power and stay pledged, jump from one Power to another just when they need some particular modules or not pledge at all, but for the casual player actually stay pledged gives more advantages than disadvantages.