"you lost compile-time type checking" makes it sound like you haven't been using code generation? Varlink has an interface definition language which makes everything type-safe.
The main use-case is different: gRPC and Cap'n'Proto are designed for networked servers, while D-Bus and Varlink are designed for local IPC. Varlink is a lot simpler than other alternatives.
That's not true in general. Many mailing lists accept emails from unsubscribed users, some moderate them (requiring moderator approval for the first post), but I don't know of any which outright rejects such emails.
Congratulations, you've found the only opened bug report about clipboard on Sway/wlroots. It's triggered by edge cases (X11 client hanging + fcitx apparently), and most of it has been fixed already.
Are you really trying to convince people that the clipboard is broken on Wayland with this? Maybe you could start by actually trying Wayland.
>as the platform under it (the hardware, the kernel, etc.) changes to the point that it becomes non-functional.
The kernel has a pretty strong backwards-compatibility stance, so you'd need to wait a long time.
Nobody stops you from running an outdated and insecure distribution to use X11 (in this hypothetical future). Nobody stops you from patching X11 to support newer interfaces.
If you want to stick with X11, you can. Nobody urges you to upgrade.