I bet they drop by Deep Space Nine in the first episode or two as they leave Earth. It would give a good chance to meet a few characters from various different series and get caught up with what they're all doing now, without having to introduce them as full fledged characters. Cisko - Likely an Admiral by now Jake - a famous writer Chief O'Brien and Keiko - Both teaching at Academy Janeway - Likely an Admiral by now Riker - Likely Captain of Enterpirse, possibly an Admiral Doctor Bashir - Frontier Medicine somewhere in back of beyond, still chasing Ezri Quark - Still running the bar Nog - Now a Commander, running DS9 Worf - Head of the Clingon Council Ducat - Supporting Romulan resistance Tom Paris - Commander under Captain Harry Kim Tuvok - Head of Star Fleet Security and the list goes on It's fun to speculate
Here are my guesses about Picard - I think in 2381 - he goes on a new mission and leaves the Enterprise I think in 2385 - he retires from Starfleet and goes back to the vineyard. All random guesses on my part, all very random.
I think some elements of Countdown will be made canon. After seeing the trailer, I suspect the Romulans experimenting with Borg technology will be one of them. I think B-4 becoming Data may be another, though him becoming Captain seems unlikely. I also wouldn't be surprised if it is revealed that the Borg were somehow responsible for the Hobus supernova.
Janeway was an admiral 20 years earlier already, Dukat is probably a pagh wraith in the fire caves still XD
Pure Speculation... Beverly Crusher - Captain of her own medical starship Geordi LaForge - Starfleet Academy Engineering Worf - Sits on the High Council Julian Bashir - Section 31 Odo - Remains in the Great Link Kira Nerys - First Minister of Bajor Kathryn Janeway - Admiral, Starfleet Command The Doctor - Holographic Ambassador to the Federation Council Harry Kim - Commander serving under Admiral Janeway