Re: Financial models matter
All of this happens, and has been doing so successfully for 18 years now. Let's take SUSE, my employer, for example. Customers with money and an aversion to risk buy support licenses from us, we give you assurances that your bugs get fixed, we pay employees to fix the bugs and provide the features, and we in turn support the underlying communities like KDE and GNOME in various ways: cash sponsorship, hosting events, loans and donations of hardware and services like hosting. Other commercial distributions do the same, and a flock of smaller support and development houses fill in the gaps for customers' more specialized needs.
Sounds like a balanced and successful if fairly unglamorous financial model.
There isn't as much scope for individual users to directly pay for individual features, there have been more or less successful crowdfunded efforts eg the Calligra illustration tool or the Geary email client. The more organised projects gladly accept donations: https://www.kde.org/community/donations/ , https://www.gnome.org/support-gnome/