Jorge, the SI 2k is nice camera but when it comes to noise performance, I think the Red One/EpicX has better ISO performance, not to mention compactness. And those 2 things make for better underwater shooting.
I personally see the Panasonic A1 as limited. The codec is not broadcast approved, so you'd have to add something like a Nano 3D to capture broadcast quality images. Then there's the focus issue where you can't focus closer than 4.5 ft. Not to mention it's a single sensor camera.
A beam splitter, dual sensor unit with either Iconix or Thomson (etc) sensors and RAW output is going to beat it, albeit at a slightly higher cost, but the results are just higher resolution AND one can focus closer (especially with a beam splitter housing).
Yes the housing would have to be custom but something like the Patima 3Diver, which was modified to fit Thomson sensors work well. The 3DA1 is a dual lens single sensor camera, designed to be compact but the picture isn't all that great with AVCHD. Plus the FOV is narrow at 47mm.
If you want 3D, you may wish to check out the Sony HXR-NX3D1, which is the professional version of the HDR-TD10 3D camera. That's out in the next few months. Or the JVC GSTD1BUS's professional twin, the GY-HMZ1U, which is out in the fall.
Neither of these cameras have the bells and whistles of the 3DA1, but they have better codecs and resolution and in the end, it's the final image that counts. Housings can be made for cameras.