Any chance we'll ever get Raiden II (not Raiden Fighter II, just Raiden II) on here ever? I used to have it on CD but it broke. :(

I highly doubt Raiden Legacy will get an update with the game, or that we'll get a new legacy version with it and DX.

That said, you can play the arcade original on MAME, just search around a bit on the internet and you should find it.

I'd start looking for it over archive dot org, as I've found a lot of old ROMs over there in the past.

Yeah, any arcade game can be played illegally via MAME, we obviously know that.
The point of asking about it on GOG is to get a legal version.

As far as I am concerned, buying an official version then use its ROMs in MAME is also an (legal) option.