1. Time-to-V1 could indeed be a useful parameter.
With today's modern digital acceleration meters and computer power it should be quite feasible to have a computer monitor the take off run in real time too. I'd guess that it could already when 1/2 the calculated time-to-V1 has elapsed predict what the actual time-to-V1 will be, and call for more thrust if required.
2. Weighing pads on the ramp have their problems. One of them is the effect of any surface wind. Wind causes the wings to create a lift force, which can vary depending on the wind direction and aircraft deck angle. This can cause significant errors in the measured weights. This is probably one of the reasons such systems have not been successful so far.