I certainly would disaprove of a map size limit. Why not let people make outrageously large maps? I have yet to understand this aversion to 80-height maps, why not let them make whatever size maps they want to?
Perhaps a file upload size limit would suffice, but what's the harm in huge maps? If people have problems with large maps, I would suggest not playing them.
Of course some people will abuse this feature somewhat, but why not let people make 3000x4000 maps? some people could make huge maps, in which there are large stories, and expansive worlds.
If people make bad maps, then few others will play them, and if their goal is for others to play, they will learn quickly.
But, if you want to make a huge map for your own enjoyment, what's the harm, and why a restriction?
Imagine if maps like these:http://knucklecracker.com/creeperworld2/viewmaps.php?embedded=false&gameVer=&mapid=28http://knucklecracker.com/creeperworld2/viewmaps.php?embedded=false&gameVer=&mapid=195http://knucklecracker.com/creeperworld2/viewmaps.php?embedded=false&gameVer=&mapid=218
Just to name a few, were able to be larger and have more expansive gameplay.
Or, what if they were not able to be created, because the size limit was smaller.
Your suggestion follows the logic that:
if people can abuse it, it should not exist.
according to that logic:
because people can get paper-cuts, paper should be illegal.
because people can get stabbed, we can't use knives in the kitchen.
because people could get run over, cars should be banned.
so why not let people do what they want to?