So, for those of us pushing onslaught, at least at the early and mid-levels (30 through 100 pre AP reset), barriers are almost always a 'bad' choice. The DU invested in them are almost always better used on Utility, DMG, or on a problematic lane.
If we accept that premise, and especially if it holds true for late onslaught too (150-400+), I see two relevant paths:
Barriers are situational (Omega waves / EMP bait).
Barriers are in most (read: non-phased) lanes.
#1 is already feasible, so I