i know this is kinda of old but the rogue stealing powers thing was already done in Xmen vs Streetfighter. But if you possibly have the time to do everyone in the Mugen-verse, Rogue would be the strongest char. kudos to you. 
Thats kind of the idea. But here, the focus is to get comic and SF chars first. It has to be coded per each character, so its not like some random char is going to be compatible, Rogue actually has to 'know' who she is fighting (ie have the power coded into her).
If you want, you could find the part of hr coding that activates this (there will be a trigger for when the name is something, like name="Ryu" or something like that, and you could add other trigger values to that, like find the one for Ken, and add Sean's name to it as a second trigger. It will be Ken's powers, but it will occur when you absorb either Ken or Sean.
April Fools