No, Silverlight is NEVER going to run on Windows RT. Microsoft has actually killed off their own platform, thus screwing over both their developer base AND their customer base in one fell swoop. Quite an amazingly stupid move. Silverlight was one of the
best things Microsoft had created in recent years, yet Microsoft destroyed it themselves.
Why they think developers will continue to trust them to build things on their platforms when they keep just killing technologies off is beyond me.
Welcome to the ever-changing world of technology. If you're looking for a never-changing platform, use COBOL (and good luck with that one).
With the competition between major players, you have to use a divining rod, your thumb in the air, and voodoo to predict their moves.
The average lifespan of today's platforms is probably 10 years (a generation), so the fact that they will still support Silverlight 5 for 10 years plus the development cycle spun up within 4 years is a total of a 14 year commitment to the technology.
If you think you can do better elsewhere, all I can say is "Good Luck!"