One of the biggest surprises on Oasis for me was that I never waited long for an elevator. Seems to me they are huge problems on most RCL megaships (do they only have four per bank?)
But on Oasis it seemed like they always showed up in very little time. I expected that to be the worst thing about Oasis.
Anyway - about ships getting bigger I have to warn you, I am very, very good about predicting things.
I will bet you Carnival announces a 200,000(+)-ton ship before 2020. I do not believe anyone who says "this is it." Once people look at Oasis as just another ship (in about three years) and ports around the world start thinking "we want 7500 shoppers dropping in on us once/week" you are going to see plenty more upscaling.
The only thing that scares me right now is that this is the worst economic downturn I have ever seen. If this debacle was not happening right now I think we would all be saying "Oasis is great." But there is a lot of just inherent pessimism in the world right now.