I always assumed (and still do) that the only reason there is an echo of Guinan in the Nexus is because she was "pulled...RIPPED away" by the Enterprise-B's transporter. Meaning, those who enter and leave the Nexus by normal means don't leave echos behind, but Guinan and the other El-Aurians did.
I always just assumed that he was Sent to that point due to the limits of his mind as in the Nexus sent him to the time that was dominating his thoughts at his time of exit
I'm not 100 percent sure that's accurate, but that could be. In which case, there would be 2 Kirks in the nexus--the same Kirk that died helping Picard, and the one that was never contacted because Picard changed history. There also would be one Picard, and two Sorans--the one that beat Picard, and echo.