Sounds great in theory. A fun community project after release perhaps.
I used to have little qualms modelling, animating (even melee sequences), making my own sprites and producing sound packs for 1.2. But for Final, frankly the model detail, amount of animations, assorted FX assets, and other miscellanea make me groan loudly at the sheer workload, and I personally wouldn't bother customising it near as much any more. The team has set a great standard for their assets. But at the same time there is alternate stuff we will want to play around with at some point, and people will.
I'm still curious how the team intends to facilitate such custom/alternate content in detail. I think it would be nice to have maybe 3 'blank character slots' - with the necessary assets in place, you could add in a character, and configure them to the appropriate class.