Not going to happen. Not without the blessing of SEGA at least. I'd rather Analogue try and license the SEGA IP SegaCD games and just release that as several pack-in games on the internal console flash storage like Super Turrican on the Super NT. That would at least give a legal venue for licencing the BIOS. Otherwise Analogue would have to produce their own RE SegaCD Bios, and that's just not something I see happening when the goal is accuracy.
Like people might not realize this, but the "expansion" options of the 8-bit systems were because they were designed as computers. The SG1000, Famicom, C64, Apple II, Tandy CoCo, BBC Micro, ZX Spectrum, MSX, and so forth all started as computer systems. The Sega Master System was basically a consoled SG3000, the C64 Games System was a consoled C64, etc. The expansion options of the 16-bit systems (SFC/MD/PCE) were because "Multimedia" was the new thing, and they all realized that the CD-ROM was the future, but ultimately they all were half-baked "use the cd for redbook audio" type of answers.
Sega seems open to anything, including fan-made Sonic games, that draw attention to them and strengthen their brand. Getting Sega's approval on an FPGA Genesis/Sega CD/32X might be pretty easily doable, considering the garbage clone consoles they approve all the time.