After plenty on consideration, I've voted No on this. This may be kind of long; bear with me.
After some discussion on exactly how vitality works (
here, as well as on this poll), the idea in this topic seems like a further complication on system that already has some complications that I think look more like errors and/or sloppy development than solid mechanics.
Vitality does not function like a normal stat. If you get it from one place, it works one way, if you get it somewhere else, it works another. This is counter-intuitive and nonsensical.
Vitality should do what vitality does, no matter where you get it or when you get it. It should work in a consistent manner. The proposed change would only make the mechanics for vitality even more quirky.
I understand the fear that providing the additional life pool that one could acquire by benefiting from vitality on gear may be troubling to developers, and that this may throw things out of balance. So, there are 2 simple ways this could be addressed:
1: Change the formulas to make it balanced. This could mean:
reducing +life rolls to make room for additional life from vitality;
reducing vitality rolls to reduce their benefit to life pools;
changing the formula for how vitality provides life to make vitality from gear an important stat for tanks in order to reach life pools that they currently reach without it;
any mix of these or plenty of other, more fundamental changes to the way the stats work.
2: If re-balancing life vs. vitality is too much work, or if developers are just happy with the way everything works and don't want to change it ... it should really not be called vitality on gear, because it simply isn't vitality. It's only part of vitality. Call it Physical Armor Proficiency or Toughness or Thick Skin or whatever you want to call it. But sharing a name with something that provides life while it neglects to provide life is sloppy, counter-intuitive, and confusing/unwelcoming for new players.
The mechanics for vitality and life pools are the same as the mechanics for intel & mana pools, from what I can tell, so this argument applies there, too.
tl;dr - This change doesn't make sense. It further complicates a system that needs to be streamlined, instead.