So Stinc asks " Would any commercial website support a post that encourages all users to migrate to another one? "
My response to Stinc "Like how you came to STEEM and told us we are moving to Tron" ?
Why is it okay if they do it but not anybody else?
Also Facebook, Twitter, Instagram, Wordpress... Pretty much every social media I can think of, allow this completely.
So given they are asking a question, the answer is 'yes'