ATA4 is IDE, you can happily get SCSI into an A1200 desktop so (no offence to Power Flyer owners) I don't understand why anyone bothers with CPU eating IDE (they like using parallel port/USB1.0 scanners?).
DCE SD/FF is a scandoubler + flicker-fixer (it allows a flicker free Amiga display on a PC monitor) made by a German electronics company.
A lot of people use the Wizard Power Box or Goliath external power supplies. An uprated A500 power supply will still blow a fuse with a super-upgraded A1200. There are plans on Aminet to modify a PC AT/ATX power supply and use the case to hold drives.
A switch to solid state drives can reduce the juice your A1200 eats, a PPC + BVision combo in a desktop case would need careful planning with cooling in mind. Maybe removing the floppy drive and getting good ventilation is the answer.
There was a 2MB graphics card called the AteoBus Pixel-64 but not that impressive. It was basically an ISA card for the A1200.
A Blizzard 1260 + AGA can do marvellous things, that might be your safest bet until you can either consider modification or towering.
