You know what, you're right about the server thing.. that is a problem.
But I still think there'd be nothing wrong with having a marketplace, if they can sort out that issue.
I used to be one of those "have nots". Couldn't even afford the internet, UT was played at a friends place and I decided it was awesome so I worked at a chicken farm getting up in the middle of the night so I could earn enough money to buy a PC. After half a year, I did earn that PC, made a lot of maps and scored a real job. I can say I am a "have" now. But I'm a "have" that still has to work and spend time with family - if I was going to make a map, I'd want it to be worthy of this generation and unfortunately that literally takes weeks of full-time work. I can't afford to take leave from real work (don't want to be a "have not" again), but if I could get some $ back from making a quality level, I might be able to.
Maybe I'm just getting older and feeling the desperation to make a buck (and maybe you're like "fine your maps suck anyway"), but the reason I try to explain it is because a lot of other guys will be in the same situation. You might get a couple of guys that can afford some time to knock out something decent (students perhaps), but I think you'll get UT3 quality maps at most (maybe that's all you want?). I wonder how many quality maps would've come out for UT3 if the MSUC wasn't there as an inscentive (personally I was only able to make maps for it because I made enough money to eat from the MSUC!).
...and UT3 still never really took off with all that free content. Maybe the game wasn't so great. Maybe UT4 won't be so great... wouldn't you rather get it for free? (and then have the *choice* of spending money on quality post-release content, or just downloading free stuff). I still think you'd end up spending less than buying the game outright. You can wait for those nasty "haves" to try it out before you decide to get it
I'm not a fan of
real F2P because the game is generally designed to make you spend just to get the rest of the game. This isn't that - its a whole game for free and if you do *decide* to spend anything at all then you're helping out someone who's taken a lot of time to make you something good.
On the server thing - perhaps a wishlist system could help. It'd let Epic know what maps people want the most? They could give the author some $ and make it free?
Meh it's all speculation at this point anyway - maybe Epic will throw the marketplace in the too-hard-basket and just do another MSUC. Surely sponsors would be lining up for an MSUC on UE4.