Then the one company that either bucks the trend or decides to enter the market after them with a locked down and supported option wins the market by default.
Are you imagining a union without any sort of industry-wide enforcement of disbarment for professional malfeasance? That's a pretty nonstandard interpretation of "union."
Presumably, if it's a union disbarring people for doing something, then it's something the majority of its members feel strongly about. Like how, say, civil engineers feel about buildings being built to code.
Given that the union I was talking about above is specifically one that would be formed by ISVs to protect its member employees from being coerced into bad working conditions by their managers or the clients their demands come on the part of, I assume that "not having to maintain software in perpetuity with increasing labor-load" is probably one such ideological point they'd be likely to stand behind, among others. (Or it might not be; either way, I still think "union that can disbar programmers" is an interesting solution to the problems that programmers do care most about, whatever they may be.)
Remember, the point isn't to punish the disbarred engineer--they likely were coerced into the practice. The point is to signal to the companies who would attempt such coercion, that it will result in their engineers being removed from them, so they shouldn't bother. (Yes, the company's name might also be blackballed in the industry, but that might not matter to the company if they're still able to make money. On the other hand, having no engineers who would ever want to work for you, for fear of what it would do to their careers, would matter.)
