I fail to see how this compares with ABM. ABM is simply a UI layer on top of a normal B4J jetty server which allows you to write WebApps without having to write a single html tag or a line of Javascript and just familiar B4X syntax. With htmx you have to write lots of html stuff + Javascript for all business logic in your WebApp.
This htmx looks like another variation of libraries like Vue, angular etc but without the nice looking components. It 'could' probably be wrapped by BANano however I can't see any advantage by doing this over taking your favorite text editor, writing such html tags manually and write your logic in Javascript and Go.
For anyone writing WebApps in pure html/Javascript/Go I can see where this 'may' be somewhat nice (not revolutionary as these special attributes are just parsed and interpreted by their Javascript library, something the others also do. They just do it for e.g. making requests to a server). And if you want your components to.look nice, you still need to learn bootstrap or any other CSS UI framework. And after that you'll need yet another language (or two) for your business logic and/or server side.
I prefer just to use B4X for everything, but that's just me ?