This would literally erase any kind of wing support we have as we know it now - our width relies on fullbacks bombing forward to open space for wingers to move in to or just to drag players out towards them, leaving space between them and the CB, and vice versa (wingers cuts in, full back has loads of space behind him... Coleman makes me sad as he usually gets the most time to cross and his crosses make kittens cry)
It's not impossible to get two "defensive" full backs but Boberto will have to rethink his whole gameplan and stop playing 2 DM's, which I'm 1000000% for. Leave McCarthy (as Barry is getting older etc) as our most defence-minded midfield enforcer sitting right in front of the CB's just to take the ball off them and play simple possession passes (which he can do as we all know), and push one of the DM's further up, so essentially we have a 4-1-4-1, not a 4-2-3-1, with more play coming through the middle. The full backs themselves in that case don't even need to be Hibbert-levels of defensive, it's just that they won't bomb forward as often and would cross from deep instead of overlapping for no reason (at times), leaving us open to counters.
What I've just written goes against everything Roberto believes in though, so the chances of it happening in real life are slim to none, and we all know that.
Comparing the Barca/Arsenal style to ours is just silly though, as they are fundamentally different. Both teams often play in that 4-1-4-1 (in defence; 4-1-2-3 or 4-3-3 with a guy sitting deep if you will) I just described, we play nothing like that - two defensive midfielders to cover the positions of the full backs overlapping (way too) deep.