We're open to a lot of things (except "make it fully POSIX-compatible"). We're still trying to not massively break everything, though.
The sort of things we've discussed include:
- Not expanding `{}` so you don't need to quote it with e.g. `find -exec {}` (currently this is read as a zero-element brace expansion, i.e. it expands to no argument)
- Removing the `?` single-character glob because it's apparently entirely unused and is another special character to remember (in fact we've also talked about removing `^` as a shorthand for redirecting stderr and `%something` process expansion)
- Allowing `$(command)` command substitutions, which could be used inside quotes as well (long term, these would replace our current `(command)` style)
- Possibly removing the special handling we have for $PATH, $CDPATH and $MANPATH (these are treated by fish as lists, which is nice in some ways and causes pain in others)
For a general overview, see [the fish 3.0 milestone on github](https://github.com/fish-shell/fish-shell/milestone/18).