I never had plans to do Tempest beyond the Atari 8-bit. I did look at the 7800, but its 4K limit and lack of line drawing mode makes it difficult to work around. May need to do webs made up with characters/tiles instead of a graphics mode. The 5200 would need a bigger cartridge and need to redo the bank switching to play digital sounds. Could do it with no digital sounds, just sound effects. That only has 16K RAM. Tempest Xtreme and Tempest Elite uses the whole 64K RAM area including the RAM under OS ROM.
2600 with DPC+. If those are in someones inventory, I say to it. The only way some games can be done on the 2600 is with some sort of co-processing. I wonder if its possible to change the player/missile hpos, color, shape several times on each line to get 4 or more different players on each scan line.