Everybody has a clue what needs to be done with ML64 - same thing MS decided to do with it - trash it ;)
I don't care for .if macro either. Instead of that I would just stop using .if (etc) entirely.
It's important to note that it would be a very different situation if ML64 retained the ML 32-bit capabilities (like invoke and assume, etc); and HJwasm had new better features. Then it would be similar to GoAsm, Sol assembler, MasmBasic, and other systems that their users love. One could still say you're "shooting yourself in the foot" by not using (for instance) RadAsm, ObjAsm, or EasyCode, but these involve new features one has to learn, and figure out the quirks. I don't blame anyone for sticking with what they're used to and not bothering with these types of systems, even though they may be more powerful.
But in this situation, HJwasm is the "good old" assembler. ML64 is deliberately crippled. So not only you have to learn new ways of doing things, it's a big step back. HJwasm does have some new stuff, but even the stack frame option is an attempt to make it as similar to masm32 as possible. You can really tell the difference when you convert old 32-bit code. With ML64 it often requires major surgery, whereas with HJwasm it's as smooth a transition as possible.
Note, I'm not considering logistical meta-issues like licensing, support in the future, Open Source code, and so forth, because I know next to nothing about them. I'm only talking about the programming tool. If such issues force someone to use ML64, so be it; I'm glad they don't affect me.