I think it is about time we add barkskin +4 and shield of faith +4 potions to vendors. After all AC is widely considered pointless by many players past a certain point so it really won't break the game. While it is true we already have a yugoloth potion that gives +4 natural armor, that isn't the main reason people pick it up. Perhaps make these (and others) available upon reaching 400 Coin Lords favor. Or add them in with 250 the Twelve favor. Better yet, make them available for purchase in Meridia or Shavarath and give us access to +5 potions as favor rewards. Make them BTA or even BTC so Premium/P2P can't sell them to F2P. And while we're at it, let's add Resist 30 potions into the mix the same way.

Yeah, I know you can grind high-level content for them, but you never get them in substantial numbers. Given the fact that Stormreach obviously has plenty of high-level casters around capable of making these things I don't imagine it would be such a hard thing to imagine. It isn't going to make rangers and clerics/favored souls obsolete. People are always going to want healers anyway and rangers contribute to DPS in substantial ways.

If you want to do a trial run to see if they DO break the game, make them available as DDO store purchases first. Let some players run around with them and see if it has any unintended consequences. But I really doubt it. Best case scenario you add a bit more plat sink into the game (negligible though it might be) and AC might be more meaningful for some characters who are borderline effective at it already. An extra +2 or +4 to AC for when there isn't a ranger or cleric/favored soul isn't going to make that big of a difference though.

As a secondary suggestion, give us potions with maximum caster level effects. Give us Cure Light Wounds at CL 5 (25 pp), Cure Moderate Wounds at CL 10 (100 pp), Cure Serious Wounds at CL 15 (225 pp), and Cure Critical Wounds at CL 20 (400 pp). More plat sink, less time standing around quaffing potions. I think everyone wins in that scenario.