Wait until they realize that on mobile they can use accelerometer data to keep the element in the same position in space across translations of the device.
While the Silicon Valley is merely a figurative Mecca for all things tech, Apple could require people to be facing Cupertino if you want to watch a WWDC stream :D
(And yes, CSS can rotate around all three axes, so you could make a div that resists rotating your device in addition to resisting translation...)
Sometimes there is no size setting that will get the text lines on a page to fit horizontally without making the text too small to read. Making it large enough to read means lots of left and right scrolling which is annoying.
A mode where moving the phone sideways scrolls the text at a matching rate so that the experience is similar to reading a page with a magnifying glass might be handy.
Wrapping is fine on some material, but when there are tables it can be very annoying.