A new MMO in today's market could definitely still work with a strong IP behind it along with realistic expectations of market capture.
I'd love a new sandbox MMO even though I wouldn't be able to invest the same amount of time as I did when I was younger. I often see the argument from people I know who used to play games like Everquest or Star Wars Galaxies just don't have time to devote to a MMO now they are in their 30's and 40's with families, yet they still game for 30+ hours a week often hopping from one new game to the next never really satisfied from their experience.
Build a solid game with depth which involves strong social gameplay and known IP and it'll sell. Hell give me SWG2 and I'll buy a yearly sub, sorry SWTOR but I never wanted you.
Oddly enough, with me (and indeed most of my online friends), its actually the case that for the first time in a while we DO have enough time to devote to an MMO now. We were in our early 20s when we started in UO and EQ in the late 1990s and then came marriage and kids which meant less time to MMO. Now however, we have come through the other side of that, kids are now grown up, off doing their own thing or left home entirely, which means that here we are in our late 40s early 50s and once again we have the free time to put into an MMO.