In terms of accel vs. time checks, there are a couple of things here:
1. Accel vs. time is going to be simply a function of excess thrust over weight, surely. It will not indicate where you are, or should be/have been on the runway. Unfortunately, a position on the runway is what we need to know -and is effectively what V1 gives us (assuming correct acceleration), based on ambient conditions.
The question then becomes "When we get to V1 will we be at the correct spot?' Waiting until V1 to see the result will only tell you whether things are about to go badly, or not, so:
2. We need a distance to go vs. speed check, again based on ambient conditions, at a convenient point prior to V1. Unfortunately, current wisdom has seen distance to run markers all but disappear. Bugger-they were quite useful for landing as well..
Perhaps there is a possibility of an acceleration rate check, based on ambient conditions and groundspeed, driven by GPS/RAAS and triggered when the TO/GA switches are pushed on departure? Something for the boffins...
As for the 777, yes, the airspeed trend vector is very useful, though nothing is formalised regarding its use on takeoff, other than as a windshear indicator, or did I miss something? As others have said here, it's a good crosscheck, nonetheless.