Our company (737NG) just changed the SOP's for T/O and RTO to Boeing standard (Captains call to reject, F/O only states the failure).
Before the change the F/O could start engines, taxi, reject T/O, land at short runways and C-cat airports.
All these things are now captain only. Besides that we now operate with one navkit that is on the F/O's side wich means they are slowly becoming a cheaper alternative to the electronic flightbag. Not a very good trend if you ask me (and I am in the left seat).
I don't see why with proper guidelines and briefing (!) an F/O shouldn't be allowed to keep his hands on the thrustlevers during T/O.
In my company F/O's are not students but highly trained professionals (always a good line...) that can handle the responsibility. If I had any doubts about someone's capability or the situation at hand then I would just do the T/O myself.
But if the training gurus think the Boeing way is the right way that's fine with me.