I know they never were an option since the T400/T500 days and I've seen people flat out say that even if they fit, they won't work with the T440P/T540P.
There are a bunch of different stores online selling the Hitachi LG BU20N as "for Lenovo T440P/T540P" and some also claim that the Matsushita UJ262 would work.
Has anyone got a Blu-ray drive in their T440P/T540P or knows if it would work?
Edit: Saw someone claim they got a Hitachi LG BU40N working in a T440P and since that's basically the same as the BU20N, with added UHD Blu-Ray support, that means the BU20N should work fine?
Next time I see them being sold at a reasonable price I'll grab one and just try it out for myself.
Edit 2: For anyone coming across this post in the future; I now have a HLDS BU20N (HP OEM) installed in my T540p and it plays back blu-ray discs without issue.