They could allow oGCD heals proc veil also, but in some niche situations as is currently is, you can pop veil 30seconds in advance and have it proc'd just before it wears off, and allow a second veil 60 seconds later. This doesn't always go to plan, either recieve a gcd heal before it's intended, or embrace, or is just simply missed.
Personally though I rather it be press, everyone has a shield and be done instead of being convoluted compared to current tank AoE mitigation.