Is it not against WordPress T&C to provide attribution(Eg backlink) without asking the users permission?
About - Plugins
There are only a few restrictions
Your plugin must be GPLv2 Compatible.
The plugin most not do anything illegal, or be morally offensive (that’s subjective, we know).
You have to actually use the subversion repository we give you in order for your plugin to show up on this site. The WordPress Plugins Directory is a hosting site, not a listing site.
The plugin must not embed external links on the public site (like a "powered by" link) without explicitly asking the user's permission.
If you don’t specify a v2-compatible license, what you check in is explicitly GPLv2.