The ability to respec a mutually exclusionary talent node to one of its exclusions without having to essentially redo your entire spec. If connectible to the rest of your spec, it would be lovely if we could swap between grenade or “blitz” talents, or for that matter the other big mutually exclusionary talent choices like aura and ult, without having to undo the entire rest of the tree first.
Not as much of an issue with mutually exclusionary sub-nodes like ult sub-nodes, or with aura/ult nodes, but with the blitz talents they’re so low on the tree that you’d have to reset nearly the entire spec to change them around.