this is what the extra character slots and respecs are for. whilst a useful idea, it is a luxury not an essential or needed function. I dont see it as beneficial to HC unless switching had an EP cost and the function being more expensive than a char slot, as this effectively allows for doubling the amount of char slots you have.
The other thing with this is that currently we have numerous lvl cap players who regularly bemoan the need for more to do, building a templar/healer is a way forward for them for those times they cant find one for their constant dungeon runs
implementing this would take away the build phase for them which includes learning how best to utilise the potential skill sets of less familiar classes