iMacs still have a latch to swap out RAM [1]. That, too, may soon be gone. Because on the iMac "Pro"s you have to disassemble the whole unit to get to RAM [2].

[1] https://www.ifixit.com/Guide/iMac+Intel+27-Inch+Retina+5K+Di...

[2] https://www.ifixit.com/Teardown/iMac+Pro+Teardown/101807 and https://everymac.com/systems/apple/imac-pro/imac-pro-faq/ima...