I think #1 is a super solid idea. I'd love to go beyond that— I'm familiar with the tech and love the satisfaction of a more DIY approach— but other end users preclude my doing so.
The author mentions quality in big email service but only passingly mentions what that encompasses. Smooth, responsive, well-worn, ceaselessly preened, and smoothed-over end-user UIs are important. Unfortunately, the open-source alternatives are comparatively rough.
(As a long-time developer and more recent designer, I write a lot of open-source code myself. I understand that these are complex and tedious problems to solve. However, without frank critique, "Open-Source Alternatives" will always be "Alternatives.")
Every interface I saw needed fundamental design work. My recent research showed 2+ decade old interface layouts w/new features just bolted on, visually complex toolbars, menus, and lists, little editing for views and controls, and comparatively unattractive designs(, which even if it doesn't matter to you, that doesn't invalidate its importance to others.) Even this crowd— people accustomed to configuring complex applications— lament the clunky interfaces.
To me, most open-source interfaces are like eating on a diet. Your sense of accomplishment offsets the discomfort... at least for a while. End-users, however, don't have or need, that holistic view of the service. To them, the interface IS the service. DIY/tech accomplishments are abstract and indirect factors, at most. For most, it's like eating on-diet, but someone else loses weight. Attractive alternatives make that unsustainable.
So the real hard part isn't technical— it's assembling an email stack where users don't feel deprived for having chosen it.
The solution is more collaboration between design and development expertise within the FOSS. If you have a position of authority in any FOSS projects, I implore you to be open-minded when presented with interface design ideas.
Happy to talk about productive ways to engage with designers and design feedback.