Even though I have no practical use for it, I've ordered a single Panasonic brand 100GB BD-RE XL, imported from Japan, just for the hell of it. Also the disc and jewel case inserts look sexy, can you blame me.
One may say "Well, can't you burn copies of 4K Blu-rays to that?" And, unfortunately, not really. While yes you can rip a DRM-free image of a 4K Blu-ray, and you can then burn that image to a 100GB BD-R or BD-RE, due to the significant differences between pressed 3-layer discs and recordable 3-layer discs, and the lack of an official standard for recordable 4K discs, it's not really going to play back properly.
Assuming your player even SUPPORTS BDXL discs (look in your manual, most 4K players explicitly do not, and only read the pressed 3-layers), BD-Rs are too limited in their read speeds compared to pressed discs. For the original blu-ray spec, this was never an issue, since the recordable spec was established the same time as the commercial spec, but no recordable spec was ever established for 4K Blu-ray (because even by 2016 the recordable disc market was already dead in most regions, I mean, did you hear anybody complain about no recordable 4K spec?), meaning all 3 and 4 layer BD-Rs and BD-REs have the data capacity of 4K Blu-ray (and beyond, 4-layer discs store 128GB but the 4K Blu-ray spec only supports up to 3-layer 100GB media), but they are all stuck with the same speeds as standard blu-ray.
All this to say, if your player even supports recordable BDXLs, which is unlikely, then it would not be able to read that disc fast enough for proper 4K playback. 4K Blu-rays run upwards of 80-100MB/s, whereas the highest quality standard blu-rays rarely reach 50.
Which kinda sucks? But also, like, realistically one could (and I have done this exact thing) just rip the main film off a 4K disc to an MKV, stick it on a suitably fast flash drive, and then stick that in your 4K player, and it'll be Fine Probably (tested on my Sony player, everything except subtitles works, but that might be fixable if some file metadata were tweaked). There's no real market for recordable 4K discs, and the inability to do such is also seen as a plus by companies concerned about piracy (though 4K discs are just as easy to rip as blu-rays, but whatever...)
So then, what are these discs for, and why does this disc in particular clearly say "for VIDEO" on it? Well, this disc hails from Japan, and in Japan, there's actually still a fairly large market for recording television broadcasts (don't ask me why, I'm sure the reasons are plentiful and complicated!), so there are blu-ray recorders there that can utilize these 3 and 4 layer discs to record several hours of HD video.
Besides that, some r/datahoarder type nerds use them for archival. I believe 100GB M-Discs exist, so there's definitely a use case there for long-term read-only storage.
I don't have a blu-ray recorder, nor would I want one (all the models I've ever seen only accept coaxial inputs, no HDMI-in), so I really do just want the One Disc purely for the novelty of it.