I've noticed this is one of my few sites that's still using the "old" profile page. Is that by design or has the change just not happened yet? In case you're seeking opinions, I prefer it over the new one, and hope we let it be!
I don't know why we don't have it yet but I'm sure we will eventually, but we haven't made a decision not to have it or anything.– Cascabel ModApr 19, 2015 at 20:40
I believe it's going to be rolled out to all sites apart from Area 51 and the only reason the release has been staggered is because of changes needed to upgrade the CSS style sheets. There's a summary here of which sites have been done already and which are planned and that includes Seasoned Advice:
List of communities with base css updates completed
I don't think there's any plans to be able to keep the old profile page, although if you click on the activity tab the view is reasonably similar to the existing profile page.