Well, I'm going to disagree with everyone else....
The Fuji X-T10 is a nice camera! Use it!
There is definitely no advantage to going with the Sony RX100 (of any "Mark"). It's a non-interchangeable lens camera. With the Meikon housing for your Fuji, you probably won't be able to use any lens except the kit lens that comes with it. But, you'll still be just as well off (better, actually, I think) with the Fuji in the Meikon housing as the RX100 in any housing.
The Meikon housing is only around $250. Their wet wide angle lens is less than $200.*
I have an Olympus OM-D E-M10, which is a micro Four Thirds mirrorless. A slightly smaller sensor than the X-T10, but reasonably comparable, overall (as compared to an RX100 or a TG4). I use the Meikon housing with the Meikon wet wide angle (and 2 strobes). Here are some pictures I took with my setup:
WSS2017 by Stuart Vernon
I don't see any advantage to you to be gained by going with an RX100 or a TG4. Other than, if you want to shoot macro, the TG4 MIGHT do a slightly better job for that one specific thing.
Otherwise, I think you'd be flushing money to do anything but just get the Meikon housing and start shooting! The Meikon housing is cheap enough (in the grand scheme of underwater photography gear) to be almost considered a throwaway item. It will let you develop a lot of really good experience, and then you can decide from there what you want in your next u/w rig. Plus, you'll have more money to spend on strobes. Good strobes will serve you well with your current camera and transfer directly over to your next rig.
*Disclaimer: The X-T10 housing would require their square wet wide angle dome port. You would NEED to check with Meikon to verify they have some wide angle dome that will work with the X-T10 housing. If they don't have a wide angle port for the X-T10 housing, then never mind. You probably don't want that housing if you can't get a wet wide angle for it. I.e. no wide angle == ignore all that junk I just posted. In which case, I'd suggest either the TG4 (cheapest option) or an RX100 Mk II (good and still inexpensive) and a Meikon housing for that. The Mk II + a Meikon housing shouldn't be more than around $750, total. And you can definitely get some dang awesome photos with that rig (and the right strobes).
The Fuji X-T10 is a nice camera! Use it!
There is definitely no advantage to going with the Sony RX100 (of any "Mark"). It's a non-interchangeable lens camera. With the Meikon housing for your Fuji, you probably won't be able to use any lens except the kit lens that comes with it. But, you'll still be just as well off (better, actually, I think) with the Fuji in the Meikon housing as the RX100 in any housing.
The Meikon housing is only around $250. Their wet wide angle lens is less than $200.*
I have an Olympus OM-D E-M10, which is a micro Four Thirds mirrorless. A slightly smaller sensor than the X-T10, but reasonably comparable, overall (as compared to an RX100 or a TG4). I use the Meikon housing with the Meikon wet wide angle (and 2 strobes). Here are some pictures I took with my setup:
WSS2017 by Stuart Vernon
I don't see any advantage to you to be gained by going with an RX100 or a TG4. Other than, if you want to shoot macro, the TG4 MIGHT do a slightly better job for that one specific thing.
Otherwise, I think you'd be flushing money to do anything but just get the Meikon housing and start shooting! The Meikon housing is cheap enough (in the grand scheme of underwater photography gear) to be almost considered a throwaway item. It will let you develop a lot of really good experience, and then you can decide from there what you want in your next u/w rig. Plus, you'll have more money to spend on strobes. Good strobes will serve you well with your current camera and transfer directly over to your next rig.
*Disclaimer: The X-T10 housing would require their square wet wide angle dome port. You would NEED to check with Meikon to verify they have some wide angle dome that will work with the X-T10 housing. If they don't have a wide angle port for the X-T10 housing, then never mind. You probably don't want that housing if you can't get a wet wide angle for it. I.e. no wide angle == ignore all that junk I just posted. In which case, I'd suggest either the TG4 (cheapest option) or an RX100 Mk II (good and still inexpensive) and a Meikon housing for that. The Mk II + a Meikon housing shouldn't be more than around $750, total. And you can definitely get some dang awesome photos with that rig (and the right strobes).