You don't understand. The mod tools already exist. To make a mod, you need three programs:Do "the mod tool of skyrim" work like the following,
create any model on 3dmax/maya/other software>>>import into mod tool>>>mod tool will mod the game file so that we would see custom mesh and textures?
start the mod tool>>>point to certain file>>>extract mesh/textures from game file?
1) Fallout 3 archive utility - it extracts models in .nif format.
2) NifScope - it allows to extract .obj from .nif, so you can create your own model with proportions, similar to original Skyrim models. For example, the sword. You'll be able to create it not too big and not too small. Also, NifScope helps you to create your own .nif file. You just open .nif of for example daedric sword from skyrim, replace parts of the sword, replace textures, and save with other name - so, you have your sword's .nif file.
3) Creation Kit - this is a very powerful tool. There you create an object, that represents your sword. Then you associate it with your .nif model. All is ready. Also you can create an object that contains ingredients for creating sword in the game, to pump your sword, etc... You can even create a script for it. For example, I made a script, that adds a Shout, that slows time, when you equip Dagger of Time. When you unequip it, shout disappears.
So, everything you need for modding, already exists. Everything you need - models.
BTW I can't even imagine the way to create acrobatics in Skyrim. I have no skills in creating animation and I don't know how to add such functions in Skyrim. But I'm sure there is some way to that.