I have 135GB of UT3 maps alone. There was no lack of content; it was markedly less in number than other games in the UT series for sure, but still significant.
The issue for me with UT4 will be the filesizes! I will have to get another multi-TB HDD for all the stuff that will come out. That the engine and editor is free will make a frenzy of content. There is already a lot out there but once this game goes full-on live, it will get really insane.
The thing to remember with UT4 is the reason it is around at all. We can believe that it was first and foremost a gesture to the community, but that would be disingenuous. First, it is a marketing tool for Epic, UE4 and the company in general. That isn't a bad thing at all, but that is the truth. Second, it is an experiment in collaborative development with a community. Third, it is an experiment in financial viability in the new age of software and finally, it is a game, one that Epic not all that long ago said would never be made.
For these reasons I think the 'point' of UT4 is very clear and there is a lot - I mean a LOT - riding on its success. To be honest, if this development drags out too long, I wouldn't be surprised to see Epic put the whole darn team on it to get it done faster (many reasons why I think this: to get a major UE4 title in the wild for gamers and potential devs as a flagship [they do want open maps with vistas for a reason: UE4 is not just a corridor/map shooter-maker], community development will certainly slow down over time, Epic will want to get the thing out the door just to 'get the thing done already!', and to maybe get some monetary benefit from the marketplace, fans will get tired of following the minute changes in the alpha and eventually reach the 'call me when its done' stage, etc...) .
One thing that I can't help but think is that Epic should (have) get behind the remake of Unreal. "Remake" has so much connotation, but Unreal could be "re-imagined" even; a proper sequel. It has much more potential in showing what UE4 can do, would bring a great single player experience back to the Unreal series and would without a doubt be well-received across the board and maybe have more overall appeal than another UT will to gamers in a general sense. UT4 could be like botpack was to be; arena modes released after the fact and maybe even solely community-driven. I may now be rambling, but to me re-making Unreal with 'botpack' development as a sub-goal just seems like a better overall decision. Yes, nonsense, I know, but interesting to consider.