It does seem to me like the author doesn't expect to sell many more licenses and perhaps wants to wind down his work on it. This can definitely endanger a project (especially previously a one man show, bus factor and all). But instead of a fairly certain death, they have chosen to give the community a chance to keep working on it, which can succeed and help make Nebulosity the de-facto standard in its category.

This is not a category of software that I'm familiar with, so I don't know how Nebulosity compares to its competitors, free or proprietary. My intuition says that 71,000 lines of C and C++ code is manageable for a person or group with the right motivation.

One thing that puts a clock on it in the intermediate to long term is camera support, which I gather from the README is a significant maintenance task. The project will bleed users if it doesn't support their new cameras.

Edit: it looks like Nebulosity sold for $95. Some other software in this space I see mentioned on the Cloudy Nights forum are Astro Pixel Processor (€ 165), PixInsight (€ 165), and Siril (free).

Yeah, like OpenOffice, or Blender, or Java, or UQM.