I think it could be less specific, in its generic form, but its difficult to make it really generic, without losing most of what makes it great.
Lets say I want to play MRQ Middle-earth. Out goes the barbarian background (probably as written), probably the primitives as well, witches, (human) wizards and those peculiarly Gloranthan descriptions of elves. The reliance on runes as a basis for magic, primitive and bronze age technology in the weapons department, and I'd have to make some rules for mithril armour and famous weaponry, etc.. Divine magic, well, it would need an overhaul, and sorcery would be ok as a basis for eastern or Mordorian cultures, but the power would come from a divine origin, (Melkor), rather than a shinto-esque view and a lot of the spells would have to be rewritten. There arent any what you would call cults excepting for the Sauronic influence, and not many places of powerful worship are highlighted as an integral part of life. A lot of the bestiary is Glorantha specific too, Gloranthan trolls as well as those elves and tuskers. The Crimson Bat isnt applicable to any other world, and neither is The Mother Of Monsters nor Brindithum.
So, a new set of backgrounds, new equipment details, new proffessions, new magic system, different ways of integrating gods into the mythos. new races, or substantial changes in the existing ones, (hobbits and orcs are pretty close however), and voila!
Now, if I wanted to play Glorantha, I'd just open the book and go.
So, hmm, not a very generic set of rules, really. Thats not to say the basics cant be used, and that there isnt a great versatile rpg in there, (Ive successfully used RQ for most, if not all, of my role playing games over the years), but, MRQ is Glorantha-centric, no doubt about it.
Therefore, I would recommend, a specific set of rules for Glorantha, a set for the Young Kingdoms, a set for Tir Na Nog, etc., without having to refer to so-called generic rulesbooks. You can use the engine for lots of games, (its probably the best around), but you cant have Runequest without the colour, it just aint possible. It too specific in its basic assumptions.
Just my opinion.