How will htmx help to inclusively solve the app side of things? Given the objective, hotwire seems like the simpler, more inclusive way to solve this, but I would be happy to see you argue otherwise.
Htmx is super-simple to get it work. Zero setup, literally.
I can't make work the simples thing on hotwire. In my mind, is like htmx=vue and hotwire=angular, ie: one is truly simple to use, integrate and is orthogonal to your current stack, the other is his own philosophy & world.
Not saying hotwire is bad, just that it like is part of a setup.
Htmx literally don't care about your server-side thing.
if you are starting from zero knowledge of any server side technology and want a front-end/back-end integrated solution, rails + hotwire or laravel livewire will be better
But from my understanding, Unpoly manages to achieve almost the same thing that Turbo + turbo frames can do, plus some other extra goodies such as modals (now layers), forms validation, etc. I honestly like Unpoly a lot more, and it also works with any backend framework "as is", given it does not require any special behaviour from the backend. That's a big win in my opinion...learning a tool that can be used everywhere can't be a bad thing.
The only thing I miss in Unpoly, is something equivalent to Stimulus. You do have "compilers" which allow you to attach custom JavaScript to any Dom element, but everything you do there is pretty manual and imperative. For these use cases I also use Alpine.