I don't see Tom as Solo either but then again, there's no reason why they'd have to keep the character the same as played by Robert Vaughn. Indeed, they may pull a MI and change the names of the main characters (or kill Solo off!).
It seems an odd choice for Cruise, given that he already has his spy franchise based on a 60s tv show. Of course, this is likely to be lighter-hearted than MI (but might that remind people of Knight and Day, where he also played a tongue-in-cheek spy?) and they could further distinguish it by setting it in the 1960s. Then again, IIRC, Soderbergh walked away from the remake because the studio wasn't willing to spend the extra money that was needed to make it a period piece. Having said that, if you land Tom Cruise as your leading man, it probably allows you to put more money into the movie.
I think Jon Hamm would be a perfect Solo but he's not yet a proven blockbuster leading man. And no doubt he doesn't want to be typecast as 'the 1960s guy'!