What I could expect in the final season:
The CMC will eventually get those marks but not in the course of two episodes or just pulling out an Alicorn Twilight either.
What I envision:
A FAST FORWARD into the future, where Scootaloo, Applebloom, and Sweetie Belle are all grown up and have their marks, but conveniently covered until the right moment, where they decide to huddle and recall the times they had together as they embark a trot back to Ponyville. And just as the main 6 explained how they got theirs, we will see the same on each one of them leaving the best for last (Scootaloo's obviously, as with Rainbow Dash). I don't are how it will be written or what will it be included, this is a sure way to explain how they will eventually get it. After the future stance has passed, we go back to the present, where the trio are still trying to get their marks, but us already know how it will happen.
Close the gaps already. Why is there a castle in Everfree Forest? How did Discord came to power and why Celestia wanted him "reformed"? What about the Gate of Tartarus Twilight stated casually while concentrating on a silly goosechase about a possible future? What became of Gilda, who is Trixie in reality?
I DON'T want to see a "Lesson Zero" -like episode now that Twilight is an Alicorn. If she is going to bother in taking this Princess thing for real, let it be in a better way and not based on fanboy MEME expressions. Of course it would be cute and funny in the way FiM has been doing, but not to lesson zero extremes. That is enough.
A major antagonist that doesn't suck please. We have 4 Alicorns now and even an Alicorn Amulet which could become a Wildcard to add in another Unicorn. There should be a menace worthy of having such power against it besides using the Elements.
Cut the Pinkie Pie scenes by half at least.
A Fluttershy/Applejack pairing episode since they are but the only pair which I am yet to see an episode of.
Make Gilda return and let the writers do anything about it. Surprise us please.
No. More. SINGING. Unless it really fits and sparsely as when the Season 1 started. Not a nentire episode musical like that mess to end S3.
Another Luna episode would be nice.
If there are Elements of Harmony, then there are Elements of Discord. A nice story tying up this sort of premise would be neat.
Make Rainbow Dash join the Wonderbolts already, but also a situation where she would have to choose between her friends and the team she longed to join since young.
Finish the entire thing, and I mean the entire series overall, with a two part episode with NO cliffhangers and NO questons unanswered. Go wild but with taste. Make us remember MLP FiM the way we remembered good shows when they ended their run.