That works because its a diamond, Hamsik can play there because its more of a CM then anything else (though I prefer playing Giovinco in the whole instead of Modric). But in a 4-4-2, Hamsik would be out of place and not have much of an impact, in anywhere else but a CM position, as a box to box midfielder.
That formation is more of a diamond in Milan mould, would prefer Modric to play as a regista in Pirlo role so to speak, and leave trequartista role to Giovinco. If we play that midfield, which I love the look of (with Giovino there somewhere), then we need absolutely GREAT fullbacks, mainly offensively.