I have been wondering about this myself. My site is still 100% RQ III related and as yet I have not scraped the cash together to obtain the new RQ books.
However as it is mostly setting related, I am sure conversion to MRQ should not be too difficult. From the top of my head one would have to review any PC/NPC stats and references to magic, although I tend to go for low magic so even that should be pretty simple.
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