I remember being so excited about this book that I diverted precious pocket money away from Attack of the Clones tie-ins to buy it.

(The wait for paperback editions on these was excruciating.) As a Trekkie kid coming right out of the nineties, the question was always "What about the Eugenics Wars?" There have been several interpretations since, but the combination of established 20th century Trek figures with real life history was just amazing.
I remember being particularly taken with the idea of all the time-travel castoffs ending up in Area 51, resulting in the creation of what was (by then) an anachronistically advanced spaceship. (That said, I was a little confused that there were definitely pictures and a model in Rain's office of a DY-100 in Voyager's "Future's End", which doesn't seem to jive with the notion that it was a top-secret ship. [Yeah, I know she also had a Talosian action figure, but I think a little more thought would have gone into the DY-100 set dressing.] I don't think that was addressed directly in the text, even though Rain shows up at some point--Greg, can you help me out here?)
2. If you had the opportunity would you try to work in the characters from the 20th century episodes that aired after the book was written?
Oooh, it would be neat to see...not exactly a revised version of these books specifically, but a deeper dive into this version of the Eugenics Wars. There was a lot of set-up for Khan and (what we would come to call) the Augments, which was important, and sci-fi spycraft, which was essential for the Gary Seven/Roberta Lincoln side of the story, but it was a little light on the 1992-1996 era of the Augments. Stavos Keniclius was left out entirely.

(I know that the animated series isn't always approved of or allowed for tie-ins, but these books had so many references to other franchises that his absence is even more notable.) There's Khan's super blood from ST:ID that could use a reasonable explanation, and the removable cryopods from that movie. (Okay, not a plot point, but the nitpicky side of me wants an explanation.

) I think Christopher introduced the idea that these Eugenics Wars were another one of Future Guy's Temporal Cold War plots, which just makes so much sense. And I know Strange New Worlds did a bit with Archer's ancestor who fought in the wars (and Keniclius!), but a greater context for that particular conflict would be interesting too.
Space Seed just makes the Eugenics wars out to be this huge thing; and from what I remember, Greg's books just didn't fit with my interpretation of that. But I can see why the Eugenics wars were written the way they were.
As much as I prefer the nineties-as-we-knew-it-compatible version of the Eugenics Wars, I get this. Especially the closer we get to the 2060s; the sillier it seems to try and make Trek's account of Earth's history match our own. (DS9's Past Tense is up in less than ten years, but that I'm kinda willing to give a pass to. Their use of bulky computer terminals and giant cell phones is kind of hilarious, and hopefully Sanctuary Districts won't come to pass. But the writers did a darn good job of anticipating exactly the kind of social and economic problems we're facing, whereas warp drive and alien contact in less than 50 years just isn't tenable in a franchise that will probably last at least that much longer.)
But part of the appeal of Star Trek is that it's our own future, and it's supposed to be a positive one, so I like having the Eugenics Wars in the rear view mirror as opposed to some kind of ever-moving-forward-but-inevitable Judgement Day ala Terminator, which is one option, or in having to impose a wildly different world order and technology level on the immediate past than actually existed, which would be the other. I think the Khan "Into Darkness" tie-in comic actually took the latter route, which was interesting but not particularly compatible with the Voyager and Enterprise episodes set in the late 90s/early aughts.
Of course, the elephant in the room at this point is World War III.

I'd just as soon the 2040s incarnation of Trek introduces a deliberate timeline change that eliminates a nuclear World War III as a historical certainty and maybe moves First Contact up a century or so. (I'd at least like to imagine a scenario in which I'm in my eighties and
not appreciating the accuracy with which 20th century television writers anticipated a nuclear war in the mid 21st century!

)
TC