I did sort of infer from some comments from a Valve dude that they're working on increasing the 100 mb limit,, but its a big job as the server architecture is sort of not up for the job..
So that would be one hurdle removed.. I'm really struggling to keep the moonpath under 100 mb.. now all the creature textures are 1K instead of 2K , had to learn the FUZ thing from scratch to get the compression to work.
Also its true doing a big mod in the CK for skyrim,, you'r busier fixing bugs or struggling against the editor itself than creating the mod..
For me for instance i can't get the batched lip generator to work, (can get all the other batched stuff to work but not that) so it takes me 30 minutes to re-lip a new quest..
Also the limitations seem worst.. The moonpath is 95 mb or something, but it turned into a decent sized mod, with about 11-12 different area's , with about 3 totally new creatures (new meshes, textures skeletons etc, and over 130 voice lines with audio) And due to its size, (i'm guessing its preloaded when running skyrim) it takes a significant size of the mod "budget" and takes it into loading issues for many users. Causing the dreaded missing area's of vanilla skyrim bug..
Now I have no clue how beth precaches or preloads their ESM and esp files.. But it seems if whatever arbitrery load value is filled up, it should either prevent load, give a warning, or just load

.. but not simply load everything,but nothing completely.. (which causes big pieces of the world and npcs to be "invisible"i.e. not loaded"
Don't get me wrong the CK is epic, but it does take a looot of hours to get something good to work.. So yeh that's why you see a dropoff,.. On the other hand the dragon carriage you can drive and stuff, that's way more advanced , just like the dragon flying mods.. Authors are really pumping out more quality mods.. Albeit smaller. Its strange my dinky moonpath which is just a giant dungeon in a sens,, is seen as one of the biggest questmods in area size, whereas if you compare it to deserts of aquina its positively tiny..
So that's changed, I would have excpected a few more ambitious landscape mods;.. But its probably coming..