If the mass effect buffing system is put back in after evaluation, this will be one more thing the buffers have going for them. Honestly, I'm quite indifferent on the issue because, hey, I'm selfish, and I'm content with the way things are right now. Having said that, I don't see much of a problem with allowing for increased potency of player-made barkskin potions, or having the material components for them altered in a way that makes the potions more appealing to brew. I don't often see barkskin potions being sold by herbalists, and as far as I'm aware, many players I know simply purchase barkskin potions from NPCs. I understand the viewpoint that Druids should be the ones with the only access to casting +5 barkskin, but I also see how herbalists could stand to benefit from a change as well. I see quite a few more herbalists than Druids, so other players could stand to benefit more if there was more incentive to brew barkskin potions that stood out from those sold by NPCs currently. As aprogressivist points out, there are already quite a few means to buff AC any other caster would be able to, and I don't see the extra +1 AC currently offered only by a level 13+ Druid casting barkskin as a major incentive for playing Druids either.
In sum, I wouldn't mind seeing herbalists able to brew +5 AC barkskin potions, or changing the required regiments as suggested in the OP to give herbalists more incentive to brew barkskin potions as they currently are. Having said that, I say again I am not particularly attached to seeing any changes made (I'm selfish!), but I thought I'd share my thoughts anyway.