Yes the Africanus version was 'just' the principes right behind the hastati (and the triarii needed not be moved). The lanes themselves were filled with velites. So perhaps the first line could have skirmishers fill up the spaces?

And yes that was pretty much the formation I hoped for with the phalanx.
While we can 'easily' flank it, so can we with pretty much every formation out there. This one at least protects one side and has the other fairly well protected. And if there is cavalry it too will protect the vulnerable open side as it would take the enemy in the flank if they tried anything.