Would it be possible to allow primary domain only for visitors, while if a user is logged in, going to the primary domain should redirect to the subdomain?
Like if user is logged in sub.main.com and tries to go to example.com which is the tld mapped to sub.main.com he should be redirected to sub.main.com
I do not think this is possible right?
http://wordpress.org/extend/plugins/wordpress-mu-domain-mapping/