Ideally you'd work with 1 or 2 wingbacks (transition from 3 CB in offensive phase to 4 or 5 at the back in defense) ... that's why we need (a) guy(s) like Cuadrado. Another possibility is to let the most defensive midfielder tuck in as a CB, e.g. in future that could be Jr. Malanda (still the wingers will have to press high + track back to slow down the attack and allow us to change into our defensive shape). I don't see Wilmots ever using a 3 center back system (although these systems are gaining momentum in Serie A - known for their innovative ideas in defense) ... maybe rightly so because our defenders grow up in a culture with 4 guys at the back (youth squads received guidelines to stick to 4-3-3). However it's a damn shame that we play CBs out of position because they're also our best full-backs (especially Vertonghen ... he's a better choice at CB than Lombaerts or an in form Vermaelen). They're even required to act as attacking full-backs, yet luckily they are comfortable moving forward. In any case it's a collective effort: if they get through on the flanks either you have a FB/pushed out CB (e.g. Vertonghen) or a winger putting pressure on the guy in possession of the ball (Hazard's defensive stats are beginning to look impressive) + cover from the CBs + if necessary a midfielder closing down every area that can be exploited. PS I feel that when guys like Jr. Malanda, Tielemans, Praet, Musonda Jr., Bruno, Lestienne, Januzaj, Carrasco, etc. start joining the big boys and we can't find natural full-backs ... a 3 center back system starts making sense (from a more conventional 3-5-2 to a stretched out 3-2-2-2-1 which increases chance creation) ... we're going to have to make hard choices about which CBs, DMs, creative CMs, AMs, wingers and forwards to use while full-backs remain a weak spot ... these systems are effective against 4-3-3 or 4-2-3-1 yet our players have grown up with the latter.
For big experiments it's already too late ... yet you could imagine rolling out a 3 center back system in the most ideal circumstances, i.e. make plans for future campaigns ... knowing we have more exciting CB prospects like Bossaerts yet have little to drool about when it comes to FBs (we won't be shortstacked on midfielders, wingers and CFs too in the forseeable future ... there are even kids born after 2000 making waves). Our FA hadn't done much until 2004 - 2006 before they started revamping our youth set-up. One of their guidelines was to stick to a 4-3-3 formation across the board (all NT youth squads and I believe at club level in each major youth academy too) ... seeing that 3 center back systems are only effective against the popular 4-3-3 & 4-2-3-1 formations when your players feel comfortable in those 3 CB systems, the least you'd expect is that they have gained experience in the first squad at their clubs ... that is already an insurmountable hurdle at this moment and the main reason why I do not advocate applying it straight away ... looking towards the future is what I'm aiming at.