FMS/ILS Transitions are basically published procedures which contain vertical, horizontal and speed elements which are coded into the aircraft's FMS database. The procedures will deliver the aircraft to a position on final approach at the right height and speed to allow a transition to a normal ILS arrival. Normally this would be at about 8NM.
Some of the possible benefits are increased situational awareness to both pilots and ATC (both know the aircraft's future flightpath in advance), optimised routeings and continuous descent profiles (subject to local airspace restrictions of course), reduced environmental impact by placing routes away from populations accurately, reduced RT workload since the aircraft is cleared for the whole procedure without ATC having to issue vectoring or level instructions, etc, etc.
Trials are currently underway with limited participation at Manchester and Newcastle.
On ACARS, I think it's here to stay, mainly as an airline ops tool (how else do you get the football/cricket scores when over the Atlantic ?) but also with some possible ATC uses too.