The UEFI system partition is mounted at /boot/efi. /boot itself can be a regular filesystem, or part of the root filesystem if you have no unusual requirements.
Depends what bootloader you use. Gummiboot (thus systemd-boot) can't handle having the EFI loader and the kernels on different partitions (thus having /boot and /boot/efi separate has questionable benefits). Not to mention that full disk encryption causes problems with /boot.
That isn't necessarily a problem; Debian handles this by means of a kernel postinst hook that copies the newly-installed kernel from its installed location in /boot to /boot/efi/EFI/DEBIAN (or wherever gummiboot expects to find the kernel, I can't remember off the top of my head).
That systemd refuses to support anything other then EFI at /boot puts it into opposition with existing practice (as seen in Debian, Ubuntu, Fedora and SUSE).