[Kunzite]

LOL, I'm not sure what (still) gives you an idea that anyone builds lenses "for lab testing". There are millions of users and only two of them are Klaus and Markus. It's that different designers choose different things to prioritize within the bracket given to them by their superiors, and when they're allowed not to hold back in any way we're getting something like the Sigma 40/1.4 Art.

Nonsense, I never said they're built for lab testing. I said I have the impression they're optimized for test charts and reviews; that is, made to get peak results in such tests. Which is an understandable prioritization; but lenses purposely built for a more uniform performance (at a higher cost) won't get extra points.
Instead of just a few reviewers, you should think of the people reading the reviews. And we're back to the million of users.

Of course film was more forgiving and many lenses considered decent in that era tanked immediately after they started being used on digital, especially high pixel density. I have three holdovers from the film era in my kit (mind you, I never shot film, it's just these lenses are of the mid- to late-90s designs), and I wouldn't want to see how badly at least two of them would be annihilated by a modern FF sensor (actually I've seen what happens to one, cursorily, and it wasn't pretty).

The FA Limiteds did reasonably well for film lenses, IMO. The 31mm in particular. It's not like the "digital" lenses are automatically better.
But not long ago - and I did mention that - everyone upped their game at lens design, and even older "digital" lenses aren't quite up to par.

Well speaking of replacements... there was that Pentax 50/1.4 and, last I checked, even the 85/1.4 but I'm not sure if the latter has become available, and in any case, they don't look like direct replacements.

Direct replacement to what? The D FA* 50mm had no predecessor, as the previous 50mm lenses were budget oriented; the D FA* 85mm can be said to be a successor for the FA* 85mm f/1.4 but there was quite a gap between the FA* being discontinued to the introduction of the D FA*.
Both are in the market, the 85mm for more than a year. Both are excellent.

Somehow I don't see Klaus returning to test Pentax DSLR gear.

Yeah, too bad about that.