Valgar:
Well let me explain why a port would make financial sense:
Arcade games (just like console games) sell good when they are fresh and new. Eventually the arcade board sales will drop (as arcade operators need to make room for new games, and then there is only a certain amount of arcade operators in the first place). When the sales slowed down then it will no longer be profitable to continue manuafacturing the arcadeboard (as the second hand market drives down the prices).
At this point Cave is no longer making any money, they have sold their boards (the arcade operators are now the ones making money). And gamers who want to keep on playing Mushi will eventually discover that the game gets replaced with something new.
This is where the window of opportunity comes for Cave or a porthouse to make more money on the game. People that don't have access to an arcade or can't find the game at their local arcade anymore will be happy to buy a port. Then a lot of people just would like a port out of convenience too and to train on (not everyone bothers with superguns or cabs at home).
Basically there is a good reason we see Arcade games like Tekken and Virtua Fighter ported for consoles, it is because there is more money to make not just because they want to do it as a service.
Sure mushi may be harder to port than their previous games, but still porting is cheap compared to making a game from scratch. 2D shooters are not really the most complicated tasks to port either. Just look at for example the simple series for PS2 and PS1, the games are sold dirt cheap and still they make profit on them (even though they have lots of weird titles made in very low numbers)..
Releasing a port of mushi right now would probably be a bad idea business wise, as the game is still selling good for the arcades. But waiting maybe a halfyear or so then go for it!

I think now it would make perfect sense if Cave ported their older games like ESP Ra. De., Dangun Feveron etc..