Isn't it possible that rather than SE being completely incompetent, that maybe the devs just didn't see the need to really increase inventory space
I'm not sure how far you delve into the "underground", (and I don't mean KI underground) but pretty much anyone who's made any app/addon/plugin/etc for any of SE's MMOs can tell you just how bad their clients tend to be depending on the nature of said 3rd party app. This is even if you ignore some SE producers admitting to their faults, especially recently. "Limitations" doesn't suddenly vanish while supporting the same system that is supposedly causing the limitations. In FFXI, there was ALWAYS a need for more inventory space, which is why when the Porter Mog system came out, it actually got A LOT of people thinking why they didn't use that kind of system from the get go? (clarification: it pretty much just tells the server which item(s) you have so after it deletes the item from your character data it knows which to restore.) The only reason is the server strain back at XI's peak would have been pretty terrible prior to their hardware upgrade during ToAU.
Even in Japanese society it is generally seen bad taste to say "no" directly to your customers, but A LOT of features and changes that came to XI were stated as impossible due to "PS2 limitations", but new programmers fixing their coding is why they were able to do a lot they were recently, even "dropping support" simply means there won't be any more releases on that platform and they don't have to create multiple assets incase they need to scale certain things or even separate certain features due to the different framework they work with. For example with XIV, the PS3 gets a "lesser" version of some new features if not completely omitted, but it in no way limits them from doing anything else. However Yoshida stating they need "the PS5" to update the dye system any further beyond added colors, simply means the client design just simply can't do it efficiently - You can to this very day still edit your XIV session and have the server comply. So not saying SE is completely incompetent...it's just well known and documented even back to their single player games, their programmers....just aren't efficient lol.
Duo - I work with the PS2, PS3 and PS4 on a near daily basis, I know the boundaries of the platform because I know during optimization of one of our current projects it's VERY easy to have something underperform on the PS3 and PS4 more so than it is to basically push the system to the limit in a way similar to GTA5 (basically due to content rather than poor design.) Similarly to how Thayos said "rather than SE being completely incompetent", most developers are extremely talented, but so few pushed any of the new gen Sony consoles to the limits, because it's actually fairly hard to. PS2, in this day and age, is fairly easy to basically make it your *****, but the PS3 and PS4? Not so much and the PS3 is well documented in being rough to develop for - That's why PS4 development is so much easier, but FAR more expensive, especially now with having to essentially create two versions of your game with the Pro in mind, which I'm fairly sure is why yoshida even mentioned "we need the PS5" because the PS4 is definitely different from the PS3 in stats, but the architecture is very much the same when you get down to it.
Trust me - If the "PS3 limits" XIV, the PS4 will, the PS5 will just as continuing to support DX9 and 32bit OSs will limit this game. The problem comes down to design. As said, SE is far more transparent with some behind the scenes stuff with XIV than they were with other MMO projects (but the info is easy to find if you look) there's some questionable design choices that has nothing to do with the PS3 for example.