Useful for when deep underground and lost, as I have found myself lately lol.
I dont know exactly how potion brewing creates this as i havent progressed to learning about this yet, but would think an Ender Pearl (I think thats the one that teleports you when thrown) would be a key ingredient in this potion.
I propose a 2 part drinking method: First swig sets the return point mark, second swig teleports you to that mark.
There would only be one potion made for the effects, just need to use it twice (from same bottle). Like say you are about to embark from your house to cave dive. You swing the potion like you normally would, the bottle then goes half empty (or can stay visibly full) and an alert comes saying something like "Teleport mark set!".
Go cave dive, when done you swig potion again and port back. You can even go so far as having a popup say something like "You are about to be teleported back, do you wish to continue?" to avoid accidental porting.