Okay, it's most certain that this idea has crossed the mind of many users but unless Playmaker got a strong financial support, it don't see this happening anytime soon because it's a huge amount of work and risk for the publishers.
PM suffers from an implied negative value, where contrary to most if not all plugins that add in content or functionality and help developers, PM replaces the coder, or at the very least adds an unwanted layer and even forces him to forget about the custom C# to relearn a new "programming" tool. It's fairly niche and does not even benefit from any form of large scale promotion.
The only way to grow this into a guaranteed, comfy and regular six digits software would require pushing it to other platforms. Yet each new branch, or support, would as said above require its own team, so the margin wouldn't be that exceptional.
A push to other systems might be abated by the tool's already established prestige on Unity. Obviously the more HG waits the more they risk seeing the spot being taken for good. But languages and tools have different logics and what works well for Unity might not translate so well to others, although looking at PM, I'd say it's fairly generic enough.
Ultimately, deploying to other systems would be a question of exploiting a potential market but providing a multi-system tool provides no advantage to a software or game publisher, contrary to a multi-platform middleware that makes accessible several markets with one single centralized tool, for a question of commodity.
However, extending Playmaker to a free language or engine, that would make a big difference to small publishers, assuming the systems and languages are robust enough.
