1. Pardon my being blatantly obvious, but having the models movements be so human would make the game seem rather un-"block-y." While the avatar models still retain their block-ish outward appearance, they have too many human-esque motions for me to still think that I'm in control of a little lego dude.
2. I think the ease of getting new add-ons makes this not neccesary.
3. See 2.
4. I don't think a trailer is at all needed. This game is good enough, and most upgrades to the next "v" rarely contain such noteworthy advancements when you are up to v19 already. V20 probably wouldn't be too much to write home about either. This is one of Blockland's greatest strengths: They find a bugfix, and plaster it everywhere ASAP. One game, Wolfquest, has a stuff-load of bugs, and the developers for the game are waiting until they can push out the next huge update before letting out any possible bugfixes.
This is just my opinion, thought.