The implementation of Rune magic is a cool and fits really well in the Gloranthan setting.
I've even been toying with a mythic viking campaign but the Gloranthan style Runes don't fit.

The Runes are blatantly Gloranthan - they don't fit in a real world setting - Vikings for example have their own runic alphabet which has no correlation to Greg's Runes.

I can't see why Mongoose couldn't have bit the bullet and tailored the Runes 100% to Glorantha, rather than doing a 95% alignment and doing peculiar things with Chaos and some of the associated rune magic. We could have had a really polished example of the working Rune magic in a setting.

Or if they'd taken a broader approach and painted the Runic concepts with a broader brush to cover multiple settings.

I suppose the real question within the post is;
Will Lankhmar and the other lines which I can see springing from Runequest, will Rune Magic and the Rune set vary from setting to setting or will the Glorantha Rune set be used across the board.

There anold Viking supplement for RQ 3 then you then might want to try to find on EBay or elsewhere. Has some pretty interesting stuff if I remember rightly.