I believe the specs are written in the video description. Neptune-X 40mhz, if memory serves me right.
In any regard, you are certainly right that this project exits but for the novelty of it. There is not point in doing a proper port of DOOM for the X68000. In terms of Japanese computers there is already a perfect port for the PC98, and in general terms one is already spoilt for choice as to platforms to play the game on.
Even if someone put in the effort one a tiny fraction of X68000 owners could benefit from it since it would require a pretty hefty and rare CPU accelerator board to be playable even after assembly optimisation.
The Lydux toolchain not working is unfortunate, but I can use it in my personal projects so I am happy. I ran into a problem a while back that had to do with word sized memory alignment of structs. Perhaps that might be the source of your troubles as well. At least if you are using any DOS or IOCTS calls.
XVI with 40MHz Xellent30. Accelerators are more common than I expected. I have 9 reported out of 40 respondents plus someone with a CPU overclock. I think that's mostly Western users too. The Japanese scene could be quite a bit different.
There are several issues with the Lydux toolchain. The linker scripts don't produce correct relocation data, so Doom doesn't work. The Newlib implementation is also extremely incomplete and the work involved in getting it up to speed is no small feat.
I'm just happy that we got it to run at all. If anyone wants to get it going on lesser machines; the source is there. It gave me an excuse to learn how to use the TVRAM write and simultaneous access masks which I am now using in my own project. I also know how to use the X68 network stack now. It's useless for streaming because it doesn't have any async I/O(no async file I/O at all actually, not just sockets), all the calls are blocking and there are no timeouts for failure to read/write a socket. It's not great
On that note, networking in Doom does almost work. I tested it quite a bit against XDoom in a Linux VM but the X68 side pretty much falls over because of the limitations I mentioned.
Well, there is that of course. Maybe a wizard level coder could rewrite the inner most loops in assembly and make it playable at 40mhz.
Don't forget we are using GCC 1.40 which is not exactly the fastest C compiler out there. The 2.x series of GCC is much faster, especially once they remerged the EGCS stuff back intro the tree in the 2.95 releases.
This is the downfall that lydux's toolchain for whatever reason can't even get a NULL version of DooM running, and we have this ancient compiler version that is 100% C... There wasn't a crazy amount of ASM in the i386 version of DooM. The Jag version uses a bunch, but you'll have to port the ASM syntax and all that fun.
If it was 1994-1997 you would still have that viability window, and all the work would make sense. This is more a 'holy crap!' type thing... and it's impressive on it's own.
It also doesn't help that i386 Doom was originally built with a commercial compiler. I forgot EGCS was a thing. You're making me feel old.