I'm not an overly huge fan of this guy but he does make some very good point regading Sony's update strategy from about 14:14 onwards.
View: https://www.youtube.com/watch?v=PEAJsrfii5s
It's the standard firmware update moan by someone who has never tried to develop embedded software.
Developing embedded software is very different to creating something to run on PC - the example he gives of Animal EYE AF in video, for example.
Animal Eye AF requires tracking the eye in each frame, and adjusting the AF in response.
For the A7iv, that's a 4k image, at 60 fps (cropped) /30 fps(uncropped), while the A1ii it's 8k at 30 fps, or 4k at 120 fps - so either a much larger image, or twice the frame rate - either way, it's a harder task (computationally) on the A1ii - and it has to be done in a tiny amount of time
Could Sony release a Flagship A1iii with the excess computing capability and unused firmware memory to allow updates for new features for a few years after initial release - yes, they probably could - but that would inevitably increase the sales price, in a highly competitive market, which would reduce sales.
Technology moves ever on, and that means you have to accept that sometimes a newer, but cheaper, model may have something not present on an older model.
Could Sony do better with firmware updates?
Possibly (only someone with inside knowledge of their camera development process could answer this for sure), but even if it's possible, Sony appear to concentrate on development of new models rather than updates of existing / older models (most updates I've seen for the A7iv have been mainly linked to compatibility with the new Creative App, rather than photographic capability), as that brings in the cash to pay for it all!