I'm planning to upgrade next year... so the idea is to buy a strobe, and then change the camera.
Purchasing your dream rig in sections is a good strategy. But towing a trailer with a sports car may not be. I agree with Detonate. Camera first, strobe second.
Since it appears that you have funds available, imho you'd be much better off to focus your attention on the camera first. If you purchase a camera with manual controls (aperture, shutter, ISO, flash, etc), you'll have the capability of improving your images vs your present system, regardless of attachments. If the camera you choose can shoot RAW, imho you'll have one that you can grow with for some time. It's also a good idea to practice with any new camera before adding an external strobe.
A major part of controlling the influence of an external strobe is derived from the camera and it's manual settings. Adding an external strobe to your present system will be at best a step sideways ( not a step forward ) Due to the bulkiness and ergonimics issue, some may even consider it a step backwards!
"Auto" cameras think that they are working on land, with two feet on the ground, and shooting through air. Their underwater use imho are limited to very close macro compositions and night dives, where the background exposures are rendered black due to the absence of ambient light.
The mere fact that underwater housings are made for Auto cameras does not validate their performance capabilities....
my .02psi,
ymmv,
imho,
fwiw,
b