This is all just early predictions but I see 40k shifting slightly in several ways of game balance:
1) Psychic powers are going to appear in every army, or rather some element of anti-psyker to counter it.
2) Long range shooting is going to take a back seat to mid-range shooting and close combat. Why? A 4+ for night fighting starting turn one says, that 50% of your games are going to use these rules at some point and thus will restrict your shooting unless you plan accordingly. People being lazy creatures will revert more towards mid quarters lists to balance this out.
3) Allies are going to be in most lists, at least for the first year or two until people go back to pure lists. I suspect you will see lists on average with at least 25% to 50% of the points packed into allies. Anything more and they should be the primary army.
4) Balance will be restored to vehicles thus making mechanized a bit more balanced and easier to deal with than before where it was hard to defeat unless you expected it (thus had a list kitted to do so) or you had amazing dice luck.
5) With the changes to the deep striking chart, expect to see more of this appear in lists again.
6) Tau, Eldar and IG will be the most popular Allies. Simple Tau has Rail Guns (helps armies short on firepower), Eldar (Runes to mess up psykers for most Xenos lists, add psychic powers if missing) and IG (cheap scoring, guns and tanks).
7) With overwatch people will think twice about charging large units…
8) Move and Fire heavy weapons and longer ranged rapid fire is going to make plasma popular again and many weapon types may reappear that have been missing like Plasma Cannons and Multi-meltas.
I can voice this one though also…don’t panic! It may be a new edition but there is no need to hate it or rail on it until you have had a moment to read the rules and play a few games.
Enjoy this quiet time of newness and such as this is the best point of any edition is when it is new and fresh. Once people start trying to figure out how to break and abuse the rules in “legal loops” on the rules then it is game on, feel free to hate then.