just because someone isn't a teenager or has a fulltime job and other commitments social or otherwise doesn't make them some sort of old fart lol.
Just because someone isn't a kid doesn't mean you can call them old, that isn't very nice.
anyways I digress. But to answer your "corrected" question of "what are you grown-ups who don't have time to grind going to do when RoS comes out?"
I'm still going to be playing; in all likelihood not on as high of an MP as I do now; but playing nonetheless. Before coming onto this forum and reading about real builds and getting all sorts of helpful freebies (which would have been impossible with BoA) and shopping advice (which would have been useless without AH) to facilitate a high MP capable character I was basically able to bumble through Normal-Hell(10) and Inferno(0) with found gear; and I would imagine the same will be possible for the new difficulty level systems.
The base difficulties should still be doable with 'found gear' and worth a playthrough.
It is quite possible that the process of improvement will become insurmountable to the point that I stop playing after getting all my characters through torment(0) act 5 but so be it; I'm still gettin RoS, The Diablo franchise has yet to disappoint me; I'm fine with buying this expansion pack.
and you never know; I feel pretty doubtful about this hyped "loot 2.0" system; the idea of a system which will be good for both the kids who can grind for hours and hours and adults who only have a couple hours a night if even that seems pretty unfeasible; someone's not going to get what they want; we'll just see who it is; and I am well aware that "we" are not really the primary target audience or focus group determinant which this decision will be made to cater towards; but that's fine; I've still had a good time, and I am confident that I will get my 40$ worth with RoS, as I got my 60$ Worth with D3, and D2/Lod when I played them back in the day, and D1 before that.