Change your shell now and test - no need to wait.

    chsh -s /bin/zsh

- All the scripts that depend on `bash` syntax will still find and call bash. 
- the same bash from Mojave is shipping on Catalina and migrated users keep their old shell. 

- - -

Also, I would estimate 95% of macOS users don't use a command line and of those that do, another 95% won't have to change anything significant or at all. _(I'd wager it's more like 10% of the 1% that know shells exist need to do anything other than port a couple lines in their .dot files)_

Your prompt will change and if you changed your prompt on `bash`, the way to change it on `zsh` is no harder and no less documented than bash.

The newer shells would fail to ever get off the ground if they broke major items or caused a painful adaptation period. If you want a more fundamental change and really want a shell you need to think about and requires training and intention to adopt - try [fish][1].


  [1]: https://fishshell.com