From the perspective of a developer who occasionally delves into SQL Server I can see that there is a benefit to the stagnant nature of software i.e. I come back after a couple of years with no real SQL Server interaction and most is still familiar.

I am not convinced though that this benefit cannot be realised if the product was no longer stagnant. If the UI remained as slow moving as before but the features were tidied up then it would sometimes require zero changes in the UI (I am including command line etc. here), sometimes a few small ones and occasionally an overhaul. Most people can live with this especially when considering the benefits.

Backward compatibility is already managed on a compatibility level for the SQL Database Engine. Is it time that each subsystem has a different compatibility level? Should we be looking to allow more changes to eventually break backwards compatibility? These changes are not made lightly so should we consider them permanent breaking changes after a particular advertised time span? Do we need something akin to the product support lifecycle for features?