[Rover]

I am reading with great interest the developers' stories published by Pentax - they shouldn't be dismissed as "marketing blurb"; sure, publishing them is marketing, but the content is actual information straight from the people who worked on these lenses. A pity that others (to my knowledge) don't share similar information.

Computerized lens design is old. Even for the earliest Limited was introduced in 1997...
Obviously lens makers started using electronic computers as early as possible; before they were using human computers. But you weren't talking about mere calculations, right?
So back in the '90s the standard was computer aided design and lens evaluation using test charts. For the Limiteds, they were also actual prints (obviously they still heavily relied on computers).
Same for the new D FA Limited; as I previously said, they made a special adjustable test barrel and shot images with various degrees of controlled aberrations (for different bokeh looks).
This is a very slow, time consuming process. I won't say yet I like the result, but I like a lens maker still thinks this way.

I believe that Pentax was impacted these last years by not making true high end lenses until recently - that is, by the "DA era", or should I say, the "Hoya incident".
I'm saying that because they had to up their game in the lens barrels' design and construction. The D FA* 50mm f/1.4 for example was delayed because of a barrel issue (the initial barrel couldn't cope with the increased glass weight, leading to degradation of optical performance).
Well, everyone had to up their game - but it might've been easier, faster if you'd e.g. constantly churn out L lenses...

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It was an entertaining read, which may explain why the 43 was found rather lackluster on both attempts here in the Zone, (and that was even on APS-C, not FF!), as it was designed against the triple constraint of aperture, price and size. There's no free lunch...

That lens, besides its constraints, was designed with zero consideration toward lab testing, and it was made to be used with 35mm film. Back then I wouldn't say it was considered lackluster.
It didn't age very well in the digital era. I'd rather have Pentax replace all the FA Limiteds with newly designed D FA versions, but that's bound to be slow and expensive.

I still find things like requiring the hood to be built-in "for the lens to be always ready" inexplicable. Unless I'm talking about a tele lens with a deep hood, I'm pretty much always keeping hoods on and in the "correct" orientation, and it never gets in the way of anything. How much of a pain are these built-in hoods for using filters?

As an user, I find the built-in hood a very useful concept.
Let's take my D FA* 50mm f/1.4 with its detachable hood. If I'd do like you, keeping the hood on and in the "correct" orientation, the lens will suddenly take much more space in the bag; actually it wouldn't fit and I'd need a larger bag. OTOH the hood in the "storage" orientation impedes on using the focus ring.
The built-in hood, OTOH, is exactly as they say: you take the lens cap off, and the lens is ready. Some collapsible hoods would have to be extended if needed, but that's much easier than reorienting a standard detachable hood.

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.

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).

If these built-in hoods don't get in the way of using filters, it's better, although I'm still considering hoods to be a sort of impact protection too, and I'd rather have a detachable piece of plastic that would flex and absorb impact than a fixed piece of metal that would transfer the force to the lens's innards and bend until straightened with pliers or, worse still, replaced along with an unspecified portion of the lens barrel. That's why I'm a little leery of the built-in hood of my 14mm, though in the case of the ultrawides it's kinda inevitable if they come with bulbous front elements...

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.

The 31/1.8 looked good in the Zone, BTW, unlike the 43 and, to a lesser extent, the 77, although how badly its sharpness would fall off beyond the APS-C frame is anybody's guess. Somehow I don't see Klaus returning to test Pentax DSLR gear.