Thinking about this more, this policy change could be the first nail in SL's coffin.
A while back, I was discussing with some people on SL what it would take to kill SL. I said it would take someone making a new version with updated technology AND LL would have to institute some poilicy that drove away a large number of people who would otherwise stay simply because they had so much time and/or money invested in SL.
Well, if LL wants to drive away all the 3rd-party viewer people who have proven to be innovative and have a good grasp of the technology, while also driving off everyone who uses those 3rd-party features like RLV, they're laying the groundwork for both these things at the same time. Some of those people who are making viewers for SL might decide to just make their own virtual world with their spiffy features, plus maybe updated technology like better-integrated mesh and a better physics engine, and all the people who want them and can't use them in SL will leave. Before long, SL is a ghost town.
Maybe LL is just tired of running SL and wants to quit?