i'm not exactly sure what the requirements should be, but here's my 2 cents:
i think we should be able to re-spec, but not a total re-spec
i think we should just be able to remove 1 perk at a time for some kind of requirement, which i guess would have to be gold.
maybe make it so it costs like 1000 gold to remove 1 perk (letting you take that perk and spend it elsewhere)
then the next time you want to do it have it cost like 1500 or 2000, and everytime you want to do this it increases
i don't necessarily think that gold would be the best requirement, but there should be some kind of requirement, maybe a rare gem or something
the only reason i think we should be able to re-spec in the first place is because i think by not allowing us to do so punishes people for experimenting and trying new things