Uppercase/lowercase modifiers in regex seem to not be supported

Both perl and sed support the \L and \U modifiers to convert a match to lowercase or uppercase respectively:

$  echo 'cat dog cow' | sed 's/\(dog\)/\U\1/'
cat DOG cow
$  echo 'cat dog cow' | perl -pE 's/(dog)/\U$1/'
cat DOG cow

sd seems to not support the same syntax (probably it's a rust regex limitation?)

$  echo 'cat dog cow' | sd '(dog)' '\U$1'
cat \Udog cow

Could sd perhaps optionally support pcre2 like ripgrep does, using a --pcre2 switch?