Using Japanese 2.1 BIOS does not produce the boot screen and play the Space Harrier theme

[RetroInVitro]

Adding the proper BIOS (MD5: 24a519c53f67b00640d0048ef7089105), setting the region to JPN, saving and reloading the core does not produce the Japanese SMS 2.1 BIOS as demonstrated in this video:

https://www.youtube.com/watch?v=uzi7VJfhtEA

[sorgelig]

Core doesn't support BIOS for SMS (yet).

[TheDatadrainer]

When will it be added? Is there plan for it?
I've seen somewhere it was already done. Using a firmware dump renamed to boot.rom, then launching the core should launch it instead of the embedded one but I never got it to work.
SMS (E/J/U) firmware contains nice things and it is sad to not be able to access them. So please, think about it, that would be great.

Edit: Maybe this request can be merged with Issue #77. Checking the issue, I found it was the place were I found the information about boot.rom at first. Which was maybe an option in the past, but does not work today.