Hopefully I'm not repeating whats already been said. I've put on my nomex undies, and here goes.
If a dive shop is going to survive the next 5 years, it's going to have to understand that it is not primarily a retail sales business, but a Service buisiness. As the computer business learned a decade ago, hardware is a commodity, and centralized, large volume e'tailers will always have internal benefits of scale that no local shop can hope to.
If a future shop has an inventory, it's only there as a specialized service to it's clients. The services that come to mind are training, rental/test dive, repair, and community. A creative owner could probably figure out that their facility might have uses outside diving to augment the revenue from their services business.
Another model which might work is that the LDS, doesn't stock anything other than what the mfg's send for "test driving'". All orders are overnighted to the customer or store. The mfg's can even arrange with some of the carriers to do their actual warehousing and drop ship (HP does this now with UPS)
I'm sorry, but I've been down this road with other markets (computers, books), and this genie ain't going back in the bottle.
It probably means some, otherwise good, stores won't be able to adapt and will shutter
jim