I want to remind Fans that Oda decided to remove 2 Chapters from East Blue just so that he ends East Blue Saga in Chapter 100!
So this should tell you how much Oda values these Milestones & Numbers.
Also the Color Spread is the Post-TS Version of the one from Chapter 100 & the Title seem to be connected too
So what happened in Chapter 100?
Dragon got Introduced + Straw Hats Vows to accomplish their Dreams + End of East Blue Saga + Roger's Quote
So what should we expect in Chapter 1000?
End of Something + Stand of Heroes + Introduction of Someone (In Chapter 500 we also got Introduction of Rayleigh) + Statement Tease
So IMO we have Answers for all Four & Oda purposefully took his time & dragged things just so he can Draw these Four Scenes in Chapter 1000! And they are:
1. Luffy, Zoro & Kid reach Roof & face against Kaido & BM (Similar Scene to Kid's Alliance vs Kaido)
2. End of Act 03
3. Introduction of Rocks D. Xebec
4. An Important Statement about Will of D.