Gief Kickflash 1200 (a rewritable kickstart flashrom for A1200) as Gulliver said or something like: http://www.terminal-entry.de/romflash.html
It would seriously rock to be able to put 3.9 Updates + Morelibspace of AfA OS not to mention modules that u use without being to rely on Blizzkick or custom Kickstart EPROMS that need lotsa work to be able to work as intended.
Imo accelerators are not so much needed to be produced since you can find very easily on eBay or even new @ GVP. Just make a need 1230 in either EAB or Amibay and you'll have lotsa replies.
Auto switching between RTG and AGA would be really cool also, although AmigaKit must have a lot of BMONs to sell (I have one and it rocks).