Anderson Silva could definetly be an average K1 fighter like win a few then lose a few. Apart from Silva, Gegard Mousasi(with a top standup trainer) and Melvin Manhoef could make some noise in K1.
Machida I would like to see fight just simply because I dont think I have seen him take any damage in UFC, even against Sokoudjou.
Without a doubt though I can definetly see Matt Hughes making the transition and he would probably win K1 MAX every year.
Melvin Manhoef already fights in K-1.
Machida he fights with a passive style and thats a foul in K-1 so unless he fights aggressive he would lose it.But i would like to see him nonetheless
As for hughes he actually has to have stand up skills which is average at best, and he would never win a K-1 Max GP.