The cards from Secret Lair: Stranger Things will be legal in Commander. Like with any cards, they’ll be judged on their individual merits. If any of them demonstrate that they’re unhealthy for the format, we’ll take appropriate action.
To clarify, Friends Forever is a limited-scope, partner-like ability. Any two creatures with Friends Forever can be your commanders. They do not interact with creatures that have the normal partner ability (Rule 702.124a).
Although we’re not the biggest fans of mechanically-unique, limited-availability cards, the folks at Wizards of the Coast have improved their processes, making the Secret Lair drops more available to more people for longer–especially since the cards will be getting Magic IP equivalents starting in Streets of New Capenna. We strongly encourage them to continue this trend.
If you’d like to talk about any of this further, we’re happy to invite you to the RC Discord server’s #format-philosophy channel for good faith discussions.