On stability

That's what "unstable" versions of distributions are for; users of those distributions will happily do the testing for you, and report a pile of bugs either upstream or by way of the distribution. That still doesn't explain shipping the (modified) source code to umpteen libraries in the application source tree.

"Handling things correctly" doesn't mean "test with every obscure Linux distribution", or even "test with the top N distributions". It means "make sure it builds in whatever reasonably up-to-date distribution the developers run, handle shared library versioning sanely, document the list of build dependencies, let Linux distributions package it, and work with them when they report bugs to you".