True, Moon Design are producing Gloranthan supplements of the highest quality, but they are meant to be used with the HeroQuest system, and they are set in Third Age Glorantha.
But an excellent piece of news has hit the "d100-sphere" today: renowned MRQII authors Lawrence Whitaker and Pete Nash are teaming up again to produce a new edition of RuneQuest and supporting supplements. This new edition of RuneQuest should hit the shelves in 2012. It will be the 6th one after two editions by the Chaosium, one by Avalon Hill, and two by Mongoose. Apparently (information is scarce at the moment), the new RuneQuest will cover both Second and Third Age Glorantha.
Loz and Pete have created an ad hoc company for their endeavour called Design Mechanism, but they will closely co-operate with Moon Design.
More information can be found at the following links:
EDIT: Loz has posted the following on the rpg.net forum boards today:
[Answer to a question re: RQ6 v MRQII] Rules and mechanics cannot be copyrighted, so our work will build on MRQII although the words will obviously be completely new. Plus, the system will got fully reviewed, revised, tweaked and the few broken-ish bits fixed.
[Answer to a question re: RQ6 v Glorantha] The RQ6 core rules won't be set in Glorantha at all. They'll support Gloranthan adventuring, but they'll not specifically use the setting. One of the beauties of our partnership with Moon Design is that we can bring RuneQuest back to Third Age Glorantha, which couldn't have happened under the Mongoose licence, so you can expect to see some Third Age RuneQuest books again in the future, as well as some Second Age. We haven't battened-down a Glorantha plan yet - there are other priorities - but rest assured that Glorantha is on the radar.