You could quite easily write a script that does this:

    #!/bin/sh
    cd $1
    shift
    exec "$@"

It's a shame "in" is a reserved word, because that'd be a good name for it. Maybe "cde" for "cd-exec":

    tar c files | ssh dest cde /some/dir tar x

The form I usually use is (cd TARGET && COMMAND), including the parentheses to make it a subshell. That seems close enough to not be worth adding features to something as simple as cd, given the basic shell philosophy of composability.