Blockland's popularity remained stable for over 3 years without a single update and a 3000 or so brick limit. You can't tell me the game is going to be "deadish" in 3 years, especially with the frequency and variety of updates. Well, you can tell me, but I won't believe you.
The mods produced now are way more unique then the stuff produced on the beta as well. Back then it was good enough to pull a free vehicle model off turbosquid and copy a vehicle script for it, or mod an ak47 to shoot a billion bullets and release it as a "new and innovative firearm." Now we've got complicated game modes, weapons with multiple firing modes... I mean, for quite a while the only custom gamemode for Blockland was fortmod, and it basically modified the entire game permanently - you couldn't build normally anymore, you were stuck in team fort mode until you reinstalled the game. BLM, AIO, basically every major mod had some kind of basic DM mode. It wasn't until the very end of the beta's lifespan that we got cops and robbers, racing, mountain climbing, rpg and zombie modes. Now people crank this stuff out every few weeks with some new awesome groundbreaking mod coming out every few months. The modders today are either more talented (I wish I could say the same for the mappers, haha) or the new game made it easier to mod. Probably both. Despite the limited nature of the mods on the beta and the total lack of updates, it stayed popular for several years. Imagine what the future of Blockland holds now. The moddification discussion forum is full of lots of cool projects. If even one of them gets finished, there's a good chance of it becoming the next big thing.
I think the stream of updates and the active modification community will keep the game alive for a long time.