Just ran the update as it has been a few hours since any packages were synced to Testing. Successfully rebooted & logged into Plasma without any issues.
I do have one concern regarding a possible typo in /etc/makepkg.conf.d/rust.conf.pacnew.
There is a new, uncommented line: RUSTFLAGS="-Cforce-frame-pointers=yes", which is replacing the commented line #RUSTFLAGS="-C opt-level=3". Should the new line actually be RUSTFLAGS="-C force-frame-pointers=yes", with a space between the -C and force-frame-pointers=yes?