alright so... uh... hmmm
I think this means I can attach my engineering brigades to divisional hqs directly
I can't think of a reason to do so. Engineers are used for two things:
1) (Originally) they're the factory equivalent of an automated mine, i.e. they add to your construction capacity as if they were a factory, but don't require any people to run them. As such, they're useful to give your initial population on a colony world a production boost, or for putting together prefab PDC on colonies on uninhabitable worlds. Note that they only work on things while they're deployed (outside a PDC), so you don't want them inside with the division commander training.
2) (Recent) Once installations have been discovered in ruins by Xenology teams, they're used to bring the installations online. Since I haven't found any ruins since this change went in, I can't comment on this one, but again they probably only work when they're deployed and so there's no reason to put them into a brigade or division.
So in summary, Engineering brigades aren't really combat units - they don't gain any benefit from being in a division.
John
