I tried putting together a 4-3-3 based on the current squad, it's a bit difficult.
Coleman-Jagielka-Distin-Baines
Fellaini-Gibson-Pienaar?
Mirallas-Anichebe-Jelavic
Some square pegs in round holes there (Pienaar, Jelavic) and not much depth to speak of at all, especially in the midfield. I mean, a 4-3-3 would be difficult for a player like Osman, and if Fellaini leaves that means we'd need at least 2 more midfielders. Perhaps Barkley gets one of the forward spots, though he's really a midfielder too.
I can kinda see why Martinez, at first glance, doesn't want to change much. It will take investment to play another way imo.