Better just stop embellishing the meter's ratings. With counties allowing the import of the shit, the markings basically are worthless anyway.
Very true, but IMO some of the markings are 'worthless' in a different sense as a result of the obsession with mains power, transients and arc-flash. A completely non-mains derived source would appear to be CAT 1, but what is the hazard level of something like an 800 volt electric car battery or a 950 volt DC solar array? Does CAT 1/1000V sound sufficient? The fuses in the meters that I actually use -- including the ones I put in my old 8505A-- would appear to be sufficiently rated to not go nuclear on the DC solar array, but the battery would have me wondering what the maximum fault current was. It would certainly give the 10kA or 20kA DC interrupt rating a good verification test.
For the vast, vast majority of these meters there is little to no chance of them actually going near any actual arc-flash hazard as defined by IEEE-1584. And that's probably a good thing.
Not being a safety buff, I don't have the background required to answer your questions. My guess is that when the standards were being developed, very little was being done with DC. At least not to the scale we had with AC and that's were the concern was. That said, I don't think they make those HRC fuses both AC and DC rated for the fun of it. I would imagine designing a fuse for 1000V DC with a 30KA fault current came with a bit of research and cost.
I would imagine anyone working with high voltages and high energy levels (AC or DC) knows what is required and has the proper training. Myself, I am not an electrician and its rare I am involved with anything that's a concern. Again, when I do, I use a meter with no fuses. Clamp only. For home, I just want the a meter that is robust enough that when I do something stupid, the meter doesn't go to the recycle bin. This is why I test the meters at very low levels.