> However I still do not really see how this is a limitation *in practice*.
Lets take a real life example: the situation right now is that the first sector of the first disk is loaded, after that the ROM BIOS hopes for the best after jumping to the first instruction of the MBR.
The "first disk" is where the BIOS can be a bit configured, there is most of the time a boot menu where you can select what the "first disk" is, and if the first disk is not readable (disk broken or any other reason), then the next disk is tried.
Something nobody planned 30 years ago happens: disk sector sizes are going to increase from 512 to 4096 bytes per sector.
With current systems you hopefully will still have the first sector loaded (for any sector size one can imagine) and one can hope that at least the first 512 bytes are correctly loaded, and it should be sufficient for the bootloader to manage the situation (I tried to make that possible with Gujin, but cannot test because those disks are still under NDA).
Now, I believe EFI will handle 512 and 4096 bytes/sector at the SATA interface, but in few years there may be something else - and because EFI is IHMO too "intelligent", to boot you will not just need to upgrade a package in your distribution, but you will need to upgrade your BIOS.