The one thing I don’t like about Assist pipelines is that they are fixed to a single language. English only speakers probably don’t care about this, but for everyone else, removing this constraint would open up a lot of new possibilities.
For example I use my voice assistant in Croatian. I could use it in English, but I refuse to, it just doesn’t come naturally.
However, I would really like if the assistant could reply in English. The main reason is that there is really a limited choice of Croatian TTS voices, and they don’t sound so great. And the ultimate goal is to have it reply like e.g. Darth Vader, HAL, Yoda, Bender… Of course none of these voices exist for Croatian. Even if they would, it would just sound stupid.
Currently, I use the Astromech integration for TTS, as an alternative, since it pretends it has support for all languages. And yeah… I even prefer the R2D2 gibberish over the Croatian TTS voices that are available 
They aren’t completely terrible, but they sound too robotic and choppy, pronounce some words too fast, can’t swear properly etc. I would rather use a normal English TTS over them, since it sounds more fluent.