I was just thinking about it, and entities disabled by ionic damage have basically been damaged by an EMP pulse which fried the electronics. In which case, they should be unable to move or regenerate shields, but the rules only say they are unable to attack, moving or regenerating shields is not mentioned. Are disabled entities still able to move and regen shields? If they are, was this a conscious decision due to gameplay considerations, or has the dev team simply not gotten to it yet?

They still regenerate. I'm not exactly sure the thought process behind not turning off regen for disabled entities, though knowing the antiquated way that regen works I would guess that it's more of the latter than the former.

Yep it is just difficult to disable shield regen, primarily in terms of database performance, right now. It will be updated eventually but it's low priority for the time being.