There is a documented psychological effect that people tend to be more upset over losing something than they are happy about finding something of equal value.
I think that is at play here. It is only one developer choosing to hedge their bets by making a compatibility layer so their software runs on a different platform. It can be argued that is totally sensible like having lifeboats on a ship.
I for one am glad that Tunetracker has decided to hedge its bets with another niche OS rather than just go with Windows, Macintosh, Linux. Similarly, those of us who support niche OS should be encouraging people to choose one that meets their needs best rather than saying it must be Haiku or Genode, MorphOS, or whatever. If we insist people can only be loyal to one OS, then we guarantee they will go with one of those that are seen as too big to fail.
Rather than worrying about the potential loss of one developer, imagine if one percent of the developers on Windows, Macintosh or linux were to spend time coding for any of the niche OS. That would dwarf the number of existing third party developers on any of these small players, and is what we should be aiming for.