I'm pretty sure I've seen it mentioned that the DCC module line will be the support for the DCC RPG, and meanwhile Master Dungeons will continue as 4th Ed. products, but I'm too newly awake at the moment to track down the mention... At least as of something fairly recent, the line is planned to continue.
As for any sense of how many MDs per year, I have no idea at all.
Theres a whopping two 4E products that came out this year. Crime Pays, which is nice but something I don't need, and the DCC Caves of the Crawling Lord, which I'll pick up at my local store.
The MDs haven't come out since the summer of 2009
so I'm not exactly holding my breath waiting for them anymore. Not since Revenge of the Dracolich fell off the schedule anyway. Much as I liked how this line started I don't know why GG would keep releasing anything for 4E now especally with the DCC RPG getting all the love now.
Mr. Doyle, I'm really sorry to hear that you don't know when its coming out either. My gaming group was really stoked to play this one. The last two Punjar modules were the best 4E DCCs, with Scions of Punjar being our favorite, we had a blast with them. Hope to see a new adventure written by you soon.