One of the highlights of Bleach TYBW episode 14 was Shunsui Kyoraku meeting Ichigo's friends. While it's not unusual for Soul Reapers to visit the living realm every now and then, the appearance of the new Gotei 13 Captain Commander, Shunsui Kyoraku, in the Human World, had more reasons than what was revealed.
Shunsui Kyoraku was handed the heavy duty of being the Captain Commander of Gotei 13, after Genryusai Yamamoto's death in Bleach TYBW. Therefore, a Shinigami of his stature, coming to the human world to meet Ichigo's friends, surely had deeper implications.
Apparently, In Bleach TYBW part 2 episode 1, Shunsui came to the Human World to tell Ichigo's friends about the possibility of them parting with their friend. However, there was more to Shunsui's words than what was revealed. This particular conversation and the true reason behind Kyoraku's meeting with Ichigo's friends were elaborated on in a very popular Bleach light novel, Can't Fear Your Own World, by Ryogo Narita.
Disclaimer: This article contains heavy spoilers from the upcoming events of Bleach TYBW arc, and Can't Fear Your Own World novel.
Shunsui Kyoraku's words to Ichigo's friends in Bleach TYBW were only half-truths
In Bleach TYBW part 2 episode 1, Shunsui Kyoraku arrived at the Human World to tell Ichigo's friends that there's a possibility that they might have to bid farewell to their friend, Ichigo. He informed them that Ichigo, to save the Soul Society from impending danger, had gone to a place to train which was exceptional, even within the Soul Society.
Even though Shunsui had faith in Ichigo that he would eventually return from that place, what worried him was the manner of power he would obtain from his training. Depending on the nature of Ichigo's new power, it could have devastating effects on the human world. If that were to happen, Soul Society wouldn't let Ichigo return to his home.
However, it was only a slight possibility, as Kyoraku mentioned in Bleach TYBW part 2. Being a Captain Commander, and someone, who holds high respect for the Substitute Soul Reaper, he wouldn't let Ichigo's friends stay in the dark. Therefore, he gave them Soul Tickets, which would allow them to visit Ichigo, had things go wrong.
What Shunsui told Ichigo's friends in the first episode of Bleach TYBW part two only contained half-truths. Of course, if Ichigo returned with overwhelming power, it would have been difficult for them to let Ichigo return.
However, even the Captains have a high amount of Spiritual pressure, and they have the means to control them or prevent that from leaking out and causing massive destruction to the Human World. Therefore, Shunsui's words had deeper implications than initially thought.
The real reason was revealed in the Bleach light novel, CFYOW novel
In the Prologue to Ryogo Narita's Bleach light novel, Can't Fear Your Own World, the actual reason was revealed. The novel, Can't Fear Your Own World, takes place after the events of the Thousand Year Blood War. Yhwach, in the Thousand Year Blood War arc, absorbs the Soul King and gains immense strength, capable of seeing and altering the future to his will.
Despite that, he was defeated, at the end of the arc. However, it's noteworthy that Soul King acts as the lynchpin. In his absence, the three worlds, Hueco Mundo, Human World, and the Soul Society, would collapse.
After Yhwach's defeat in the TYBW arc, the Royal Guards stepped in and cut Yhwach's body into several pieces, and placed the main body in the Soul King's place. Since Yhwach had absorbed the Soul King, his remains would have been the perfect alternative to hold the three realms.
Ichigo's hybrid nature, i.e., his having the powers of Quincy, Soul Reaper, and Hollow, made him the perfect candidate to replace the old Soul King, after the events of Bleach TYBW.
In the prologue to Can't Fear Your Own World, a conversation between Kyoraku and Ichibei confirmed that Ichibei intended to make Ichigo the new Soul King if Yhwach had killed the old one. In CFYOW, Ichibei said,
"That young lad caught my interest too. I would have been quite beside myself if he had rendered silent."
However, the fact that Yhwach absorbed the Soul King, and his remains acted as an alternative, Ichigo was let go. Shunsui, in Bleach TYBW, mentioned that depending on the type of power Ichigo gains, it may affect the world of living. In that case, the soul society wouldn't allow him to return.
One might say that Kyoraku knew that there was a possibility of Ichigo becoming the next Soul King since he fulfills the criteria to become one. Kyoraku was relieved that his fear didn't become a reality.