It seems as though the INON UWL-100 and dome unit combo is still the best available compact camera w/a solution (other than the UWL-165) and it works very well with the G9 and a short port.There are w/a solutions for the G10 but none approach the 130 degrees of the INON glass. For me, this double underlines the dominance of the G9 over the G10.
On acquiring my first G9 a couple of years ago I quickly realised that swapping lenses during a dive was not a practical proposition on three counts. Firstly the size of the UWL-100 and dome. What do you do with this chunk when its not on the port? Secondly, M67 threads are very fiddly and are a recipe for a dropped lens or cross threading and thirdly, INON UCL close-up lenses are best used with the long port which rules out using w/a glass.
So my dives are dedicated to either macro or wide angle which I believe this has an advantage as I can enter the correct 'mindset' of either and focus accordingly. Sure, I miss a few shots but I'd miss more by trying to juggle M67 lenses.
The new generation of IXUS Canon compacts and their ability to use the UWL-165 AD bayonet would seem to address the issues of the G9 and G10. If I were investing in a compact system today I would give these cameras serious consideration.