At the moment, the make-thread-local procedure is invoked as

(make-thread-local default [inheritable?])

When the last argument is missing, #f is used in its place, meaning a
non-inheritable thread local.  I wonder whether it makes more sense to
create inheritable thread locals by default.  For example, the
make-thread-parameter procedure is also defined in terms of
inheritable thread locals.

Thanks for looking into this,

Marc