Personally I wouldn't touch page transitions with a ten-foot barge pole.
At best, they distract from the content. At worst, they just make the creator/presenter look bad.
Page transitions on PDFs are a bit like flashing text and marquee scrolling in HTML. They were a gimmick that had their day in the sun but should now be retired in favour of more "mature" ways of doing things, I.e. Just go straight to the next page.
If you think you might need page transitions to make your content interesting and keep the viewer engaged then your content isn't interesting enough. Don't paper over the cracks, fix the cracks.
I think it would be a good idea if the Extras tab in the Export dialog was removed completely. I can't believe there's more than a tiny minority of people that actually use these things and it's extra code that needs to be kept up-to-date and tested which will take up valuable development time which could be better-used elsewhere.