Proposal: "Some third party cookies treated as first party"
No. No, no, no.
Cookies were designed with a privacy mechanism. Third party cookies are a deliberate attempt to circumvent that privacy.
When said vulnerability was realised, if it wasn't for the vested interest, the flaw would have been fixed.
Only now are browser makers looking to address the problem. Anything else, no matter what weasel words are used is basically again trying to take advantage of the original flaw.
No third party cookies, period. (Yes, I know it's still possible to have the same functionality with first party cookies, but it requires more effort, and shows obvious intent to do so, which will be more important thanks to GDPR and general improvements in user awareness)