It's no big deal to learn that new syntax. The problem is re-using old code. Converting 32 bit code - either ML, JWasm, or asmc - to 64 is not bad with HJWasm or asmc. But it's much harder to go to ML64. Sure, you "just" change ">" to "}" - although you can't do a global change, must consider each one individually. No big deal. But how many such are there? The worst part is stripping out perfectly good code, for no good reason. My favorite example is "ASSUME". You can't merely change those specific statements, but must make a lot of little associated changes. If there were a good reason for it, you were buying some new capability this way, it would be Ok. But the opposite is true.
Similar problem arises for those of us who continue to use both 32 and 64. With HJWasm, or asmc, it's very easy once you get used to it. Most of my code works with either 32 or 64, leveraging a few obvious "IF" statements. Sometimes code makes sense only for 64, as when making extensive use of the extra registers, but that's rare. And of course you use the same assembler for both. With ML you need both old 32-bit assembler and new ML64, plus the right auxiliary files; and the syntax is quite different. Forget about "one-size-fits-all". And, BTW, every time you upgrade to the latest ML64, you're going to need a new set of auxiliary files.
If there were no alternative to ML, it would be annoying but one would take it in stride. But (I can tell you this from experience) the worst part of using ML64 is that half your time is spent asking yourself: "Why don't I just use HJWasm (or asmc)? Why am I wasting my time with this? I hate Bill Gates ..." and similar unproductive thoughts.
Oh well, hutch, I hope it works out well for you and other ML64 enthusiasts. If you can avoid the above-mentioned unproductive thoughts, because you feel there's a good reason for using it, it shouldn't be too bad. Maybe time will prove you right. Maybe Bill will create an effective anti-HJWasm-and-asmc virus.
BTW the worst part of HJWasm and asmc is having to write out "HJWasm and asmc" instead of simply "ML64".