Serious question, how did you weigh up taking the "SSL" out of the book title?
On a positive note, I was able to add "PKI" to the title, which makes sense because the book is actually about PKI as much as it is about TLS. A win-win, I think.
TLS 1.3 is definitely a good breaking point. If you understood exactly how SSLv3 works, you could read TLS 1.2 and say to yourself OK, this is basically the same protocol except with some fresh paint and with some extra gadgets I needn't care about yet, whereas you just can't do that with TLS 1.3.
I also see you put TLS 1.3 first, and I think that's a good choice, show people the Right Thing™ as we understand it today first, this is not a history lesson.