I suggest considering some type of soft luggage, not only if you might do a liveaboard. We used to use hard luggage for dive trips and eventually changed to soft rolling bags. I got these when we were about to do our first liveaboard, as the hard stuff was in sad shape anyway. There are bags that are mostly soft but have hard bottoms and sometimes partial sides or special construction to give more structure to the bag.
I've personally found soft to work better for dive gear - it just seems to be easier to fit gear into the more forgiving shape, and our hard luggage overstuffed with occasionally damp stuff didn't fare too well after awhile. I pack some clothes and other things in the bag wih the gear and pack carefully. I've never had anything damaged. I do carryon regs/masks/computer, but more because I want to make sure that stuff gets there. The hard luggage might seem to offer more protection, but there's something to be said about a more forgiving bag, something that "bends not breaks." I was always expecting to see it come off the plane in pieces.
Another advantage of soft luggage is it tends to be a little lighter, so when you're filling the bag with a bunch of gear it helps to meet airline weight limits.