Introduce a new approach to automatically disable maintenance of units #5822: This is an energy throttle order that you can issue to units to make them turn on/off based on energy. It would give pause icons to fabs and give players full control over throttling. Unfortunately it was left unfinished with Jip working on many projects, then leaving the game team, and nobody picking it back up.
There were also some changes concerning stored energy. Fabs still toggle off at 80% and on at 90% storage but now there is a 105k storage limit above which fabs wont turn off, and a 108k storage limit where fabs are forced to turn on. It's mainly for overcharge but if people know about this they can cope with fab behavior by building a pgen-storage 2x2 for 16 storages and rather efficient energy.
There were also some logic changes to make fabs aggressively use energy overflow from allies when on lower max storage.
I disagree with @deribus's eco analyses. The problem players have with fabs is that they can never use up their storage. For example, if you have 100k storage and try to up RAS (only 175k energy) you lose out on a few seconds of a few fabs instead of using up storage. Basically you're forced to float energy with the fab behavior.
This is due to the assumption that you need to store energy for OC combined with no existing implementation of adjusting your energy throttle parameters (which goes into my next point).
Desyncs aren't a reason you can't have user-adjustable or permanently saved settings for fab throttling. To implement that it's as simple as writing a sim callback that sets the parameter for your army's ai brain, which is no different from toggle resource sharing or adjusting diplomatic status or toggling auto OC and so on for nearly every UI feature we have. The only difficulties I foresee is if you're playing with union control then you have to determine permissions for adjusting throttling, and writing the UI to show how much energy youre throttling and syncing it between players switching armies or on the same army.