I think AmigaKit mentioned before that the main obstacle to implementing an ATX PSU converter for the 2000 is designing a TICK signal generator. (I have an mini-ATX PSU in my 4000, and it's great!)
While browsing the A2000 Schematics I noticed J300, which selects between the TICK signal from the power supply and (the schematics are in another room, so I'm relying on recall here) the VBLANK signal.
Would it be such an issue to use the VBLANK signal in lieu of the missing TICK signal from an ATX power supply? Wouldn't that only make a difference with the internal clock when the system is in a video signal mode opposite of its native mode (PAL->NTSC, NTSC->PAL)?