This is Linden Lab's worst decision to date. The SL default viewer is a sub-par experience, poorly programmed and tremendously laggy and cumbersome. By hindering third party viewers, LL is ensuring that they will alienate a large number of users, we will continue to see a decline in numbers.... and I don't need to be Nostradamus to point towards what that will entail for Second Life.
Very poorly played, Linden Labs. People have been able to provide users with superior products. Instead of acknowledging their superiority, you are crippling them so that an inferior product is used more.
This must be what business looks like in Looking-Glass Land.