Unlikely to happen, but permanent conversions to 3 car formation would make for an ideal "long distance" fleet for Scotrail post central belt electrification. Six car trains, with through-corridors, and end-vestibule doors, running to Inverness and Aberdeen? Would be far too sensible...
There will be very little demand to make such fleet modifications
The current proposal is to reduce the DMU fleet to Class 156 and 170 on completion of electrification
Class 156 will cover GSW and WHL
Class 170 will cover the remaining routes (although there are issues over using Class 170 between Aberdeen - Inverness, and north of Inverness)
During the next franchise a replacement for the Class 156 will also be required
Several options are being explored which includes a new express DMU (also 3 car) which would then cascade the Class 170 to replace the Class 156
The main issue is the WHL, this will be the base requirement