I know this is something I would be interested in.  Heck, I've started manually converting maps in Photoshop!  I'm very fussy about skin textures and I've seen very few for V4 thus far that impress me like some of the best V3's.

Also, money is an issue.  I can't justify buying a fistful of textures for V4 when I still use her so rarely.  A remapped version might be the trick.  I ended up getting plenty of V3 textures because they also worked on Aiko, The Girl and S3.  Heck, they even work on the guys!  I don't know if that is something I'll ever use, but I like the freedom.

I would be very curious as to what DAZ would say, but I think that if you go through their License agreement with a fine toothed comb you might be fine.

I think if you ask them outright, they might say NO.  They had the power while making V4 to make her use the excellent textures on the market, but chose not to.  I'm sure there is financial reasons behind that.   (ie:  selling new textures).

On the other hand, they might say yes but want you to sell it through them.  What do I know?  I need coffee...