I'm making a list to stop the multiple suggestions that are currently impossible or were posted one too many times.
►Buildable cars - Although it is a good idea, it'd just be really, really complicated or really, really laggy. Or both.
►Add-ons based on other games - Although it's a change from the usual edited machine gun, people don't like the idea.
►An add-on edit - Nobody wants to download five of the same things that just look different, unless it has different features.
►Acrobatics - The engine the game runs on makes rotating a player on its (which one?) axis impossible.
►Brick Physics Ideas - The physics engine Blockland uses does support that kind of thing, it would need further engine changes and you wouldn't be able to interact with it on the server.
►Copyrighted Mods - Nobody wants a Wall-E mod, just because you say "LOLZ MAEK WALLE MOD ".
►Reuploading - Either the author of it did not like it, because it was handicapped. Or the add-on was failed, and shouldn't be released until fixed.
►Any more ideas?
Also, you should use proper spelling while suggesting something. Not many people would know what a "lit saybur" is.