As for designing to the reactions of players. Sure that would work great if you only made a game for one person, but each and everyone one of us, even here, have a different defintion of what is fun to them. Hell we all can't even decide exactly what an CRPG is and we are a RPG only site. That makes it a little difficult for any developer to react and adjust to the community.
Don't developers already design these games with players in mind? And don't modders as well? Abandoning the concept of single version would only enhance that effort. It could be done poorly, sure. But that's nothing new, is it? As is the case already, the trick would be to do it well.
For years modders have been proving over and over how single-player games can be improved, taking advantage of how they're hosted on individual platforms. It's a PC approach, really (one that would be better than the current one, IMO).
But who would buy something they know nothing about? No one, naturally. That's why I think that kind of DLC would have to be provided via subscription. Then instead of merely always adding more and more, its content could (and should) also be redundant, meaning it could be created and provided in varieties of versions that would be unique and mostly incompatible (and matched to fit the player specifically).
Only one version at a time could ever be played, of course, and that would be the key (that and what you would be left with after throwing the concept of single version out the window). Remove the player's firsthand knowledge and control over it, and modifications have the potential to make CRPG very intriguing, IMO.