If so, any standard can be changed?

Yes. Install DOS, it was 100% BIOS.

Isn't DOS in floppy disk?

well, yeah its.

If you mean avoiding OS as a separate piece of software then yes, it would definitely be possible but wouldn’t make much sense, I guess, since such a biOS would be the only choice for the customer. It would be “hardcoded” into your hardware and to replace/update it you would have to go flashing BIOS which is a very special operation.

The media is not important. It can also run from USB memory sticks. The BIOS emulates all the stuff for DOS.

BIOS and CSM compatibility will be dropped by 2020, according to Intel. It will then be UEFI only, and I somewhat doubt that most people are interested in creating some kind of shim to run such old legacy (sadly). So you're stuck to VMs for things like that. In the old days, DOS was installed in ROM on various machines.

P.S. I often run FreeDOS natively on my (2010 and 2011) machines (still having BIOS and no UEFI), and they don't have floppy drives at all (in case that wasn't obvious). In fact, the diagnostics partition of my Dell laptop uses DRMK, aka (barely-modified) DR-DOS.

Well, the quality of the compatibility layer would decrease anyway because of new developers not aware of all the compatibility quirks that should be preserved. But it’s definitely a bad idea to drop it while not having a good alternative. My experiments with UEFI made me believe its standard was written in half an hour and UEFI it self seems to be considered by its developers as “just some stupid stuff enough to prevent people from complaining we did nothing”. At least using UEFI on my laptop to draw a simple game desk turned out to be a nightmare and, without proper documentation on the quirks of its particular UEFI implementation, mostly failed.