There are different methods of doing triple+ layer Blu-Rays - all involve either getting a brand new player, or updating the firmware of existing players. None can play on any current Blu-Ray players out of the box.

I don't think triple+ layer discs will ever become the standard, except perhaps in TV-show DVDs, in which case I think it's a great idea. Imagine having an entire season on one disc, at potentially better quality than the previous multi-disc releases - that would also make complete-series sets much, much more feasible. But for feature films, I don't think it's necessary unless it's an incredibly long film like Lawrence of Arabia, or the original miniseries cut of Das Boot (almost 5 hours long).