The last time this came up (not all that long ago), it was decided that
the main mapping would be:

Lister: Ranma (No curse?)
Rimmer: Tatewaki (Hologram with a stick)
Cat: (er Pig) Ryouga
Kochanski: Akane.

Ranma is amazed to learn that his pet pig P-chan, now a few million
years passed on, was pregnant and a girl pig.

Ryouga doesn't turn into a pig.  He's an evolved pig and now enjoys
watching rugby.  (Obviously evolution can only do so much)

Tatewaki is still a fascist stuffed shirt, but at least he's just a
bunch of pixels now.

I'd like to see Kasumi as Holly. (Oh my!)

That would be quite ... amusing.

But Toufuu would have to be the original Holly, and Kasumi would be Hilly
who Holly fell so much in love with that he had a head-sex-change
operation to look like Hilly!

Kun-chan...