I wonder why you stop there, FASM, Bogdan's assembler, GNU "AS" (GAS) and whatever else. I have already seen Japheth's piece of crippleware that you seem to have abandoned, complete with its crappy c header conversion tool. You forget, I spent years being attacked by "Open Sauce" bludgers because I would not write software for their shitty licence.
While the Watcom forks will probably have support in terms of include files and libraries by the year 3000, ML64 already has a comprehensive set of both and is production capable already. I have waited for years to see if any of the bludgers would produce the support to make the Watcom forks viable but it never happened, I want a tool that is finished in my lifetime and ML64 is already finished, that's the difference and its backed up by Microsoft who use it themselves.
I only support freeware, the rest can write their own.