Personally, I think the Foundry sums up STO in nutshell.
It's fun, it has loads of potential, but its really still in Beta and we probably shouldn't all be using it yet.
In this case, I think Beta means that Cryptic reserves the right to change it as necessary and those changes might cause older Foundry missions to break. They might even temporarily pull the feature altogether if a serious enough issue arises.
But that would be true even after the Foundry goes "gold", since I don't expect them to stop making improvements and enhancements. Heck, as far as I'm concerned every MMO on the market is in a constant state of "Beta".
Now that it is on Holodeck, I expect it's usable enough for me to really start playing around with it (as I get the time).
And what else are you gonna do while we're waiting for Season 4?