Map Chaining...

I think this would be really neat. I'm sure it'd be possible to develop an algorithm to automatically detect which map bits can be spliced together (so as to prevent any impossible combinations). You could allow players to select individual map pieces, or maybe even have a "random" mode which grabs a handful of map pieces and combines them together in a random order to have somewhat randomized maps.

I want to add "Like" or "Upvote" features to this forum.

Certainly! Some sort of voting or thanks system would be great. I noticed this addon on the vanilla forums page, no idea if it's good or not but might be worth checking out.
http://vanillaforums.org/addon/likethisplugin 
I'd say you could use random mode. Maybe have the "pickandchoose" be an endgame thing. Easiest way to do it is probably just go off of the "How many players" value  for example, if the first map the player picked was "At least 2 players", then it could chain together any map with "At least 2 players" and "Any number of players". If the player picked "Exactly 4 players", it can chain maps with "Exactly 4 players" and "Any number of players".
In addition, you could have it register how many players are in the game  if there are 4 players ingame, it could pull maps from "Exactly 4 players" "At least 2/3/4 players" and "Any number of players". 
Yep! As the list of maps grows, we definitely need to start filtering better. These are all excellent ideas!