I think this is a good idea, and i wonder if it has been forgotten (since it is said to be so simple but not done after over a year)
But now to my own suggestion for limiting potions to make them more realistic:
There could be a time bar that has to fill up before the potion is finally drunk, like the little window popping up when casting a spell. For the roleplay, this time would mean: taking the potion from your inventory (and putting away your weapon if you wield one), opening the bottle, lifting it to your mouth and finally drinking it. Bigger potions need a little longer for this. You can of course only drink one potion at once.
The limitations while drinking could be almost the same as when casting a spell: it is hard to open a bottle when running, so it will be aborted if you run. You cannot fight or work while drinking (try it! make fast but controlled moves while drinking without spilling most of your drink or choking

)
But i think spellcasting should still be possible while drinking potions. If i am not mistaken (correct me if i am), magic in Planeshift does not need any gestures or spoken phrases, so drinking would not keep you from casting your spell. Drinking does not need too much of your concentration, so you can still concentrate on casting while you drink, though perhaps with a little restriction:
For example, you have a smaller choice of success for your spell. Or maybe even better: you need skills/stats to cast spells while drinking: only a strong/experienced mage can cast a spell also while drinking, unexeperienced mages need to concentrate more than someone who has cast a simple spell hundreds of times. This would mean: you need a higher level in the magic way to cast a spell while drinking than you would need to cast it while not drinking, or you need a high rank in the stat corresponding to the magic way.
Another suggestion is that healing and mana potions might work gradually, not instantly.
oooof! that text became longer than i thought. any criticism or questions?