Why are we looking for
a way? The series is going to feature species we've never seen, and I'm sure species we've met post-TOS, and it will present clever and not so clever reasons for how that works. Whatever the reasons are, they are
not going to involve stranding the whole crew for centuries, unless that was the original plot idea. While I would like a story where the crew would vanish for eons, I certainly wouldn't like a story where the plot revolves around meeting minor targets, like featuring post-TOS entities for the sake of featuring them.
And... Previous series hardly had issues coming up with explanations for this, good and bad:
* TOS: The Menagerie.
General Order 7. Nobody learned about the Talosians after that incident.
* TNG: Clues. Nobody learned about the Paxans after that incident.
* Every second episode of Voyager: “No, I can't tell you.” “Why not?” “Temporal Prime Directive.” “Yawn.”
* ENT: Acquisition did a very good job there. It might even be considered defamatory to follow-up such incident with a description of the species for future reference. (Not that a description would help, in the Ferengi's infamous first appearance they were only known by name)
* The Borg were on 21st century Earth in First Contact, then in ENT: Regeneration,
and none other than Mark Twain himself personally knew someone whose world they had destroyed. Yet we mysteriously never knew about the Borg.
* DS9: The Trill were in contact with humans in TOS, yet in TNG Dr. Crusher was shocked to meet a Trill. Seriously, who remembers all the species in the galaxy, and knows everything about them?
I'm sure the tradition here will be followed, except that Discovery will do it better.
And what are these post-TOS entities that anyone is excited to see return? The only interesting entities that cannot be featured without shenanigans are the Romulans and the Borg. And I feel the Romulans will be featured regardless of that. If the show runs long enough, so will the Borg.
Almost any other entity can either appear without any explanation, or wouldn't be interesting. (I'm looking for all those excited to see the Kazon return)