There's not really any need for that since no talents are calculated *exclusively* before an objective is started. You can start an objective and immediately level up talents before doing anything else and it'll have the same effect as starting the objective with those same talent levels.

If you're worried about keeping up with monster kills while on the talent window, you can turn on "Toggle pausing on pop ups" so that the game pauses while you're in that window.

I'm sure the devs appreciate every bit of input they get, but I wouldn't bet on this ever being implemented since it's a lot of work for something pretty small and circumstantial. Plus, there's already a method for that that works in-game. Start any free play, buy the talent, then abandon that free play to start whichever new objective you want.