Second thing to note is all the required things you'd have to do. A quick checklist just from my head:

Cyrodiil, on the map, is bigger than Skyrim. Which means the heightmap would have to be bigger than Oblivion's original one (since Skyrim is the "same size" in game terms, a matching Cyrodiil region for Skyrim would now have to be bigger.)
Increase the Cyrodiil/Oblivion Heightmap by 1.5x which looks about right. Shouldn't be that hard.
Get permission from Bethesda for the mod to use peoples (legally obtained) Oblivion assets It MAY be possible, depending on how you go about it. Again, no putting them up for download. Maybe they'd be alright with people copying the BSA's over to the Skyrim data folder, but maybe not. You definitely can't port them over to other "games" but OpenMw was allowed to go forward using the assets in a brand new engine.
Re-do all of the NPC's Brand new npc art system means every npc would have to be redone by hand. Besides, it's been quite a while (200 years?) since Oblivion. No one from back then would be alive anyway.
Reconstruct every bush and tree model No more speedtree means no direct use of the original tree and bush files. You could use the models and textures (such as you can get) but would have to rebuild all of them.
Reconstruct every town, city, and dungeon The filetypes might be the same, but with a new scripting language and plenty of other things for Skyrim it's doubtful the new CS can read the old files. Ideally someone would create some kind of exporter. Otherwise this task would be nigh impossible, or at least just very very long.
Reconstruct/New levelled lists, AI, and etc. Again, can't read the original files.

The conclusion is that, even if it is legally possible, it would be a fantastically huge undertaking. But best of luck to anyone that tries.

Bleh why would you even want to port Oblivion over... At least Morrowind was a amazing game in its own right.

But sure you can make Cyrodiil in Skyrim, but you can not use any of the items provided in the Oblivion game (meshes textures ect). That is not legal.

The original Morroblivion program would convert the files on your hard drive, so you had to both games or nothing would get converted.

That would be acceptable, but, despite being similar, the assets don't have direct replacements. You would have to redo every city, dungeon, etc, you *may* be able to get away with some things, But you might as well get a team together to rebuild it on your own.
I would like to help if anyone wants to do Morrowind.

This thread would've been locked a year ago when people asked the same thing about FO3 and NV. Pretty sure mentioning a mod to put Cyrodiil in Skyrim over on the nexus would net you a permaban

If it could be done without distributing assets, there is absolutely nothing illegal about it. Doesn't mean it won't turn in to a gray area here and lead to suppressed discussion

I bet it would be easier to put the Capital Wasteland or Mojave into Skyrim though (not that that would be easy either).

This is apples to oranges obviously (compared with Cyrodiil in Skyrim) but linking FO3 and NV is easy in case anybody cares to mess with it, the instructions are out there. After you set it up, there is a console command to get to FO3. Some things are missing though and there are explanation points in their place. There have been a couple attempts at making a mod that had a train station to link them (which eventually would create the missing things rather than porting... so it would be legal). The nexus killed that off too and banned people talking about it. But hey, if you want a furry mod they got plenty

Guys, what you choose to do on your own computer is up to you, so far as these forums and discussions on these forums are concerned there is no using the assets of one game in another, whether they be from one of gamesas's games or from an outside studio.