Accountability would go out the window with a significant increase in players (ROBLOX levels). Right now, we are such a tight-knit community that we can all watch over one another and hold each other accountable for each other's forget-ups. Games like ROBLOX and GMod with their millions of players don't even have things like the Drama board to regulate its player base. If someone does something bad there, it gets forgotten and they don't learn from their mistakes. While that may be mostly true here as well, the Drama board does convert some jackasses into good people. With a massive increase in players would come a STAGGERING increase in bad players, and it would be difficult to keep track of all of them.
The notion that development would skyrocket substantially is also flawed. Sure, there are a few diamonds in the rough, but think about how many among us are noteworthy devs right now in this community. Taking cues from ROBLOX and GMod, you could easily expect what Carlin called children; "A few winners, a WHOLE LOT of LOSERS." Also, keep in mind that most of the """""development""""" in these games is repeated copies of previously-made work. Blockland filters that out. So what do you get really?
It would be awesome to have a few more dedicated players. The levels you're talking about, though, are WAY too much for a game/community like this.