I think Bill would do it if they had a script in place that pleased him...to me that seems to be the problem with any of these attempts, there isn't a script that is of interest to him.
Since you're apparently on a first-name basis with him, maybe you can ask.
No, Murray's reluctance (and now, refusal) is due to two factors: One, he had a terrible time on Ghostbusters II
and it really soured him on the franchise. Two, he and Ramis still have never really mended their fences since the complete and utter falling out that came about because of Groundhog Day
. It's not a Cold War like it was until about 2004 or 2005, but the two are still not anywhere near being on the best of terms. Murray's a very sensitive guy, and he was very hurt by Aykroyd and Reitman on Ghostbusters II
, and he felt incredibly
hurt by Ramis on Groundhog Day
. He very clearly doesn't have much interest in resurrecting a franchise he isn't terribly fond of in the first place, especially when there's no real creative reason to do so.