I doubt their user base would grow much.
Metric Halo makes premium grade audio interfaces. Windows users who are not using Pro Tools are, by definition, the cheapest and least discerning customers in the consumer-prosumer-pro audio market.
Not all of them of course, but that's a fair description of the group as a whole. If you were less frugal and more discerning, you would have a Mac for your pro audio. And yes, it really is that simple.
Windows users also cost ten times more money to support, between driver issues on a far more diverse platform, a vastly more buggy platform, and a vastly less savvy installed user base.
This is why few pro audio companies have "gone PC" in the past five years, while several have "gone Mac" and several have dumped Windows entirely. It's also why MOTU has never seriously supported Windows, and why Digidesign no doubt would take it back if they could. (They introduced Windows products in the mid-1990's, when Apple's longterm viability was legitimately in question.)
(As a side note, it is telling that Pro Tools, Digital Performer and Logic, all Mac-oriented programs, also have excellent interoperability -- sharing DAE hardware and dealing seamlessly with OMF files, which seem to baffle Nuendo and Sonar folks completely.)
This is not to say that Metric-Halo is a perfect company, as they certainly are not. But their products are pretty damned tasty, and of tremendous value. And I can't blame them, or anyone, for not supporting Windows for pro audio devices. To borrow an idea from the TLM-103 thread, just because it's possible to get good results from a device doesn't make it a professional, quality product. That's Windows pro audio.
JSL