If an original part is unavailable, yeah, I'd replace it with a more modern replacement. I prefer that it remains functional more than keeping it 100% original. But I would still first try to find an original part. And I'd feel somewhat disappointed, and the computer would feel a little less appealing to me, if I could only find an FPGA based replacement. I know that's bizarre, and I can't rationally explain it, so I guess I agree with you in a way.
I can get preferring to stick to "real" parts if available, even though it's not something I really care about. I draw arbitrary lines too, I just generally feel it's worth being pragmatic about them if the alternative is losing functionality, which it sounds like you are too.
No it is not bizarre, it is normal and typical feeling in retro community. Check prices on Apple-I or NOS analog components. I'd say it is quite unusual to be indifferent to the period accuracy among those who are interested retro tech.
