Don't use the 8255!" without any justification.
Agreed, if you live in the past, there is no justification , but even you have, grudgingly, admitted that it is too slow to operate with modern uCs without slowing them down.
Now, attaching an old ratteling caboose to a high speed train, does that make sense? is it "justified"
You keep coming up with harebrained schemes, most of the presenting the advantages of one configuration as justification for another, but that is not the way to set in concrete, to do that you need to mix cement, not facts.

but provided no persuasive argument that the 8255, limitations and all, is not suitable for expanding the I/O of an 805x. It might not be easy to use with YOUR 805x, though I would guess it can be done
I have no doubt it "can be done" and have never argued that, but it would be outright silly to do so. That you prefer to use what you used in the stone age, is your choice.

All you've done for the past 100 kBytes is argue that the 8255 is a poor choice for this purpose. You've not presented even ONE reasonable argument why that would be, for the typical case, though I can see why you'd not want to use one yourself.
If "the typical case" is using the old moldy chhip laying around in the drawer, you are right, however, if that is "the typical case" that would be a VERY sad state of affairs.

True, the 8255's slow, but its' not too slow to use with many of the currently marketed parts that fit the 805x model.
If you do not use them to the full extent of what they are capable of

Now ... why do we keep having this argument? ... Well, it's because you CATEGORICALLY state that it's wrong to use it. You tell people who have ready access to them that they're too hard to get. You tell people using 25-year old MCU's that they're too slow. Most of the time you don't even ask what sort of MCU they're using. You just tell them that they're stupid and they should do what you say.
I don't like that.

You keep stating that using 25 year old technology is brilliant.
I don't like that.

If you gave them an informed choice, after telling them what's involved and how to find out about that, I'd be fine with that. If a guy wants to expand the I/O on his 805x, you really can't answer without first finding out which MCU he's using, what kind of I/O he wants to expand, and other things like that. Have you ever asked such questions?
yes, many times, and the answer that come back is either none or, "I have one" or "I saw in a book that this is how to do it" and if somebody were to state the purpose instead of 'how do I make the 8255 work" the reaction from me (and others) could be very different. As to "informed choice" to the best of my recollection I have always done that.

Those ST parts to which you referred
You keep coming back to that. ONCEE MORE, this time PLEASE GET IT the list included those for the sake of completeness and the list DID include the 8255

The 8255 DID sereve a purpose, I used it extensively in the old days, that is not the argument, the issue is that what WAS current technology, is not that any more.

Erik