However, it's surprising to hear that they've been focusing on UX. The fact that you have to manually install a plugin, then install a version, and then finally set it, without the tool suggesting any of those steps to you when you forgot one, really makes the tool annoying to use when switching versions a lot.
As a proof of concept I wrote a Fish native version of the function that figures out what local version of a tool to use I do actually use it to show the currently selected version in my shell prompt. The asdf version was unusable in a shell prompt.
It goes through the parent directory structure up until the top level root directory and finds the first .tool-versions file and parses out the version of a specific tool.
The asdf native shim takes ~100 ms in Bash (no idea if it can be optimized, but I assume so). My Fish version takes ~1 ms.