If you really want it, I wouldn't stop you. I don't think higher level potions would break the game. I consider potions to be expensive scrolls (they cost twice as much and have limits that scrolls do not have). I've considered letting there be wands for spells greater than 4th level. Staves used to fill that role back in DND 3.5. They had 50 charges, multiple spells, and no option to recharge them.
I might require you to do something like spell research to figure out to make higher level potions.
Yeah, I wouldn't have a problem with it. A 100% premium in exchange for anyone being able to use it at all seems like a fair trade. Smoke bomb-obscuring mist potions, grenade-fireball potions, monster-in-a-can-summon monster IV potions--why not, I say?
I allow all of this, plus drinking normal potions as a move action, and people *still* barely use the things.
Yeah, I think allowing higher level spells to be potions assuming you keep the same cost structure means nothing is going to break.
The cost double scrolls as someone pointed out, and the main deference is that you don't need to be able to cast spells to use them.
And considering that unless you have the potion in hand you'll need a move action to retrieve it and then a standard action to drink it...
Yeah, I don't see it being a problem. Really it would just allow non-casters greater parity with casters. Which I see as a good thing.