Not an issue at all with our without exec option, I think. Since we can mount a folder on itself at that point we can redefine mount options.
Next step: (re-)mount home [and other?] with noexec (and nosuid [among other useful mount options]) for better security? needs to be sorted. Help welcome.
Over next step: /usr/bin/torbrowser remounting Tor Browser folder. This could even be protected by a lxsudo prompt.