If one defines a market by measuring current sales, then there is no market because there is no SDK support. No SDK support means that products requiring the SDK cannot be created. Thus, according to that definition of "market", there is no market, nor could there ever be.
The same logic could have been applied to Pro Tools before it was created. Before the first version of Pro Tools was created, there was no market because there were no sales. Thus, by that definition of "market", Pro Tools itself should not exist today.
Please keep in mind that AAX plugins are written in C++, and would merely need to be recompiled with a Linux version of the
AAX library to support Linux. Linux has a lower barrier of entry for software developers because, unlike Windows and Mac, the compilers and libraries necessary to build programs are free and open source.
This same argument has been made against Linux by various vendors for years, with a wide variety of outcomes. Some vendors (Adobe Flash, for example) have vacillated on Linux support. Some vendors (
BlackMagic, for example) provide Linux support. In the last two years, Microsoft switched from "Linux is the devil's work" to "We are the 2nd biggest provider of Linux, behind Google Android", Linux has considerably more opportunity than ever before. (Android is a Linux distro).
Pro Tools sells to professionals, and professionals require reliable and high-performance tools. No-one claims that Windows is more reliable than Linux, or that Windows outperforms Linux. That is why Linux is the most common OS for servers in datacenters. Windows is very rare in data centers.
The past does not dictate the future. Technology and markets continuously evolve. Opportunities come and go. The Linux market opportunity has changed a lot in the last 2 years.