While I think Lyoto is a very worthy challenger, my fear for a Lyoto Rashad matchup would be that it has the potential to be pretty dull.
I really like Machida's style, it's unique and very effective. But it can be boring if another fighter doesn't decide to take the fight to him. He works best when exploiting openings left by other fighters coming forward.
Rashad is also more of a counter-puncher so either someone is going to have to take the initiative or we will be in for five rounds of cat-and-mouse with very little being landed by either fighter. And to be honest I don't know if it is in either fighters' interest to leave themselves exposed by being more aggressive than they usually would as they are playing to the others strengths then.
I do want this to happen as I think Machida has proved that he is championship material at this stage, i just think that it is an interesting but potentially dull matchup in my opinion.