If railways has final goal of running only AC trains, they should stop production of non-AC coaches now. These coaches have a codal life of 25 yrs. They should concentrate on manufacturing AC3T and AC3T ECO coaches instead of LHB sleeper coaches. They should also develop ACC version of GR/Yuva coaches (ACGS/AC2S) and start manufacturing them. We already have some passenger trains (Not M/E/SFE) with only LHB GS/2S.
Immediate goal should be to run trains on GQ/GD at 130, plus as and when infra happens, 160 ready rakes should be available. So...
more... start replacing SL with AC3E on likely routes. Once ACGS is developed and manufacturing starts, GS of those trains will be ACGS/AC2S.