Performance concerns when heavily used in scripts ?

Yes back pre-systemd, Debian and other distros explicitly switched /bin/sh to dash because it improved boot time running System V scripts using dash rather than bash, so the speed of dash definitely matters in that it was notably faster than bash once you were running all those hundreds of shells during bootup.

It'll be interesting to know how much of a difference uutils would make for running shell scripts if the startup time for the utilities is slower e.g. if a script has a loop that runs cp, ls, diff etc. in a loop. But I imagine with more use there'll be more focus on performance and startup time rather than just feature parity, so it'll improve over what it is now.