Aren't these things going to always be issues for Star Trek though? If the franchise continues for 40-50 years more, people will wonder when the Vulcans will show up in 2063 and where Zephram Cochrane is. The events in ENT are relatively right around the corner, simply the next century, that's not that
far away. Heck, how are all those things from TOS or Trek XI supposed to happen in the next 250 years or so?
If they do Khan, they can not give out the 1990s date because mainstream audiences will think "WTF?". They need to ignore the date, retcon Khan's backstory or simply not do a Khan story at all.
But if I remember TWOK retconned Khan and his people. Khan sure didn't look like a Sikh Indian in TWOK as he did in "Space Seed", and his followers went from dark haired to becoming all blonde haired Anglo looking people. How did that happen?