Star Trek: Discovery made its first reference to James T. Kirk in its season 2 finale, "Such Sweet Sorrow, Part 2." In an episode packed with references and homages to past Star Trek films and series, the Kirk reference was a subtle one, but perhaps the most important one.
While the Discovery and the Enterprise engaged in a dazzling battle against Control's Section 31 fleet, Michael Burnham (Sonequa Martin-Green) and Spock (Ethan Peck) were executing their plan to pull the Discovery - and the precious sphere data stored in the ship's computer - into the far future, where Control could never use it to conquer the galaxy. But, as often happens with these sort of schemes, things did not go exactly to plan. Burnham realized she had to travel back in time with her own Red Angel suit and create the signals that would set the events of the season in motion. She was able to pull that off, but when she returned to her relative present she found that Spock's shuttle had been damaged, and realized her adoptive brother would not be coming with her to the future.
After expressing their affection for each other, Burnham gives one last piece of advice to the brother she'll likely never see again:
"There is a whole galaxy out there, full of people who will reach for you. You have to let them. Find that person who seems farthest from you and reach for them. Reach for them. Let them guide you."
In an interview with Entertainment Tonight, incoming showrunner Michelle Paradise confirmed that line was indeed about the relationship Spock will eventually have with Jim Kirk, his commanding officer and best friend for a significant portion of his life. It's an interesting echo of one of the final scenes of J.J. Abrams' 2009 Star Trek film, where the Prime Universe Spock (played by the late great Leonard Nimoy) encourages his younger self (Zachary Quinto) to remain in Starfleet and embrace the friendship with Kirk that will come to define them both. This once again makes Michael Burnham a crucial player in Star Trek canon - albeit one that will likely never be recognized in Federation history, as the surviving crew of the Enterprise and Starfleet Command agree to stick with their story that the Discovery was destroyed, not sent to the future.
It seems unlikely we'll ever get to see Peck's version of Spock make good on that final promise to his sister. There's a growing demand to see a spinoff featuring Spock and Anson Mount's Captain Pike have adventures on the Enterprise, but Kirk wouldn't take over for Pike for another decade or so. Even if we don't get to see a new version of that relationship, Burnham will likely find out that her brother flourished in her absence - assuming there are still Federation records in the 32nd century.
Retconning Michael Burnham into Spock's backstory was always Star Trek: Discovery's most polarizing decision, and one that meant the show - and Burnham in particular - was often weighed down with issues of prequelitis. But the fact that Burnham planted the seeds for what would prove to be Star Trek's most iconic friendship just about makes it all worth it.