The core ruleset is not bound to change too much. But armybooks will be kept being developed, but at this point mostly balance tweaks. If you don't play regularily I doubt they will matter too much. We will however continue to write Full Army books (look at the newly released WDG book for a hint about how those will look), and make auxillary army lists for people to tinker with.
Does it make sense for a bunch of old lazy painters to switch their tabletop rules to T9A if they dont want to constantly check for updated rules?
Of course I know that now one is forcing us to update our rules if T9A evolves but if I do that switch I like the idea to be able to just visit my local store and play a game with the guys there without prior discussion of rules...
So be warned!!