Hi Stephe:
Is this something you're considering releasing officially? Also, is there any reason this wouldn't be applicable to lsp-mode in addition to eglot?
One of the reasons I ask is that I often find myself disabling/overriding some features of the current ada-mode (e.g., skeletons in favor of YASnippet, require-final-newline setting, etc.) or not using them at all. For example, I don't use the packaged method for building...I'm often interfacing with makefiles or have multiple permutations of the build and multiple targets/compilers, such that the built-in features don't really work well in my workflow. So, I'd probably be most receptive to a slimmed down Ada mode where I can add on the different packages I want (yasnippet, lsp-mode, multi-compile, project.el/projectile, etc.) without having to disable some of the current functionality in favor of other packages.
I don't know if other users of ada-mode find themselves in a similar situation, but I'd be most receptive to just a simple mode like this and leave a lot of the heavy lifting to other packages.