Variants can be a good thing or a bad thing. About the bad things, I don't like how the development is branched. If there are e.g. 5 variants and each of them has 4 good new features, they are better than the official version with none of these features, but worse if there was a version with all 20 of these features. One great game is better than five good, but very similar ones.
Dungeon Crawl is lucky to have the Stone Soup team, who combines the good features of previously created Crawl variants (tile version, travel patch, and vampire patch, AFAIK) and also introduces new improvements. We can treat these variants as testing grounds for new features; these tests turned successful and that's why they are added to Stone Soup (which is as official as it can get). (I would be happy if DCSS allowed playing the Zot Defense variant too.) IVAN is not as lucky, there are many variants, but it seems none of them is strong enough to become an IVAN version of Stone Soup.
Thus... I hope the ZapM variant somehow gets melded with the original.