2 issues,
The 787 is supposed to be a bleedless aircraft, now take out all the engine and apu valves and ducting as well as the ducting in the wings to the cross/bleed valves and back to the APU. Put it all on a scale and I wonder if a couple of electric starters that weigh a bit more than the existing IDG's would not weigh a whole lot less than a pile of scrapmetal that would fill a U-haul?
I understand the IDG's of the 787 are to be rated at 120kva, common volt/amp rating to atleast the 777. gear ratio has IDG's rotating at 400hz. I believe it quite possible to get an estimated 20% n2 or n3 out of as little as 60kva or less, regulate enough amperage to get her rolling and accelerating at a demand within spec. I am interested to find out more but do not believe the electric starter demand will be a factor.