Good points on all comments...
Even though I have been brought up on SLRs, I can see the day that even DSLRs will be obsolete.
The single lens reflex system is based on seeing what the lens sees before taking the picture, in film cameras. This is accomplished by placing a mirror between the lens and film plane. Which was fine, but made the lens much more complicated (more glass elements to make up for the distance, the mirror takes up.) and expensive than that of the PS or really a Rangefinder type camera.
The drawback of Rangefinders is the focusing capabilities; although the pictures from a Rangefinder will be sharper than a SLR (Due to less glass elements) accurate focusing is almost hit or miss, esp. in macro shooting.
Fast forward to the age of digital, we do not really need that mirror in the DSLRs when the technology of extremely high res. large TFT/LCD screens, are installed in the digital cameras. Making it possible for more accurate focusing (when I mean accurate I mean you can rock that camera back and forth and watch a sea slugs head to tail, go in and out of focus, in manual focus mode!).
Down the road I see a hybrid digital camera that will replace the DSLR, with the simple hi res. fast focusing lens of a Rangefinder, with the option of the removable lens feature of the SLRs.
This approach only makes sense because you cut down on manufacturing expenses, no more mirror systems to install and lower lens cost lenses due to less glass. Plus the prices of LCDs are dropping.
The Rangefinder will still be around due to the low price appeal.
Oh and the shutter lag? By the time they make this hybrid, that too will be the thing of the past.
IMHO for UW photography? Stick with the PS or the Rangefinder cameras for now. Look all around us, unless for some ultra wide angle shots. Even I can not tell which pictures are from a DSLR or PS/Rangefinder!
Dive Safe