There is still no Linux app store

"The point is we still don’t have a robust way for developers to monetise their application development work"

You can monetise your work the old-fashioned way. Open a website and advertise your wares for sale.

The fact is that Linux does have some 'app stores'. They're called 'package managers', programs like 'apt', 'yum', 'rpm', etc.

You can still donate to the developers of the APP you use in Linux. It is like an NPR or PBS model of free stuff paid for by donations from companies and individuals.

and thanks to the higher powers for that.