Accessory lens maker LensBaby has announced a circular 5.8mm for micro 4/3 cameras, among others

The Circular Fisheye is great for capturing the scale of endless landscapes and big events, fun self-portraits, quirky shots of pets or friends, creating extreme perspective, and experimenting with unique lens flare.

I am gradually moving over to m43 type cameras, and a good Fisheye is in planned list of future lens aquisitions.

This lens could certainly have good applications for underwater work, so I am going to look further into this as a contender.