A Living Version of Runequest could be fairly interesting in concept but there is a great deal of work that goes into a successful "Living" or persistant campaign.
For a little quick background, I am a Triad memebr for the Geoff Region of Living Greyhawk. In real world terms that is the Mid Atlantic United States (DC, VA, MD, DE, WV). I have been involved in two such campaigns directly, as an Editor and Author. I am by no means an expert on numbers or resources etc...
The most important aspect, IMHO, for a Living-style campaign would be a compelling story with compelling non-player characters. This allows the player to immerse themselves to a certain degree as well as allowing them to interact with their environment. This also keeps folks interested.
Second, you need a dedicated staff who can take the rules and tweak them in such a way as to create a fun, fair, and balanced environment where rewards are equal across the board. With a D20 system this is much easier to do then a % skill based system like the older versions of RQ or the BRP. It is not impossible of course, just more difficult.
Third, you need to get into the local cons and possibly sanction online play. Con goers will try just about anything AND often there are times when their favorite game is all booked. Having more Living-style options would not hurt anyone's feelings.
A couple of down sides do exist. For one, the RPGA has been going away from the Living-style of game and towards a persistant style which is much less labor intensive. Living Force is going away, Living Greyhawk and Living Arcanis both seem to be doing well. I am not sure the RPGA would find a benefit in partnering with a company like Mongoose on a persistent campaign.
On a local level I think most local Cons would love to have some variety.
A Living-style campaign is a good deal of work if you want to make it work but I think RQ is probably one of the few game with enough fan base to make it work.