All I know is this:
In 1991, my dad bought Final Fantasy II for the SNES when it was brand new. He paid $60 dollars for it. Last year, I paid $60 for the Deluxe Digital Edition for DA:I. The price point, not accounting for inflation (really beside the point,) hasn't changed since then. I figure if folks enjoy MP, then I'm happy for them! It's always wonderful to have multiple options. I don't pay more for games with them, so why not? 
I've never really enjoyed a multiplayer environment. It's nothing against the MP crowd, I just prefer taking things at my own pace. Plus, I have two dogs and I need to be able to go AFK at a moment's notice. In MP, most people aren't very patient with that. That's okay by me, since it's not on them. Most of the MP crowd I've met in games over the years are pretty nice. Even if someone enjoys PVE/SP over PVP/MP, as long as a person is respectful, it's easy to get along. I've rarely been called a "Carebear Player" (old term for PVE in MMOs) because I don't tend to call those that enjoy MP/PvP "elitists."
Then again, I tend to ignore most gamer debates. 
As far as the topic directly goes, I support the OP's idea. I figure that would be an excellent way to make sure all of us can get the most out of our games. There are folks that prefer single player and will unlikely touch MP. There are folks that feel that the ME3 story was very weak, and that multiplayer is where the game is at. There are also plenty in the middle, contrary to the staggering amount of blanket statements I've seen on the matter. If someone is having fun, awesome. Multiplayer and mods can help extend a game's lifespan. Of course, good word-of-mouth from game players you trust helps too.
They don't have to be connected, and I can see the point of view of those that think they should remain separate. However, I don't see how the OP's idea could affect that. It seems like they wanted a way to come up with everyone getting the most content that the game has to offer. I don't see any attempts at exclusion here.
For as bad as some folks think that the forums can be, if it wasn't for this site, I wouldn't have played the ME series. It's rapidly turning into my second favorite series to date. I still prefer Dragon Age, even after DA:I (that game is my #1 favorite DA game,) but ME beat out Neverwinter Nights. While I respect those that feel quite differently, I'm not really interested in debating about it right now. I just think that the OP has a pretty balanced idea. If we can all have more fun with these games, then I support it.