Even today, Solapur super fast takes less than 12 hours between YPR and SUR both ways. Add 4 hours for SUR to Pune and another 3 hours reach Panvel. Total 19 hours.
So, it is possible to run a proper Bangalore Mumbai train to cover the distance in 19-20 hours max.
If we have a TT something like YPR DEP 1530 PUNE ARR 0745 and Panvel 1100, will you not prefer? Return Panvel dep 1430 Pune dep 1830 YPR arr 1030 is possible.
Again...
more... I am reiterating, there should be a will to find a way.