I am a huge fan of McCall - saw his work as a kid at a museum and my father said that he had also love his work as a kid.
His mega strcutres were incredible for me growing up.
He used things that I had never seen before, so fantastic, later I learned they were called archologies.
It's still a fundamentally good idea, just not on the scale depicted.
Yet that does not mean that they won't be some day. Materials science is advancing quite rapidly. It will be interesting to see what we can build with all the new materials that are being discovered.
I was looking into the heating and cooling costs for large structures like airports and malls, by square footage, compared to smaller separated individual homes. It's extremely efficient, interior volume increases non-linearly with exterior surface area. It's also cheaper and simpler from a utilities standpoint to integrate them into the structure with access corridors than to bury them under concrete.
The only bad idea was building them on a scale that would require materials that don't exist. Consolidated multi-zone buildings already exist around the world, some cities in northern climates link them via an underground layer of the city to allow you to avoid exposure to the harsh weather
I feel like this is an idea that will come back in a big way when we start to feel some of the more severe consequences of climate change.
If future construction materials are rigid enough, I see no reason why it would be unstable - it would be equivalent to sticking a lollipop into the ground - provided it goes down deep enough. Think of all the fascinating buildings we can construct today that were imagined by futurists in the Victorian days, but shot down for not making sense - "An 800m tall narrow building in the desert? Where would the stairs go?!
I'll bet the rental apartments at the very top much be very cheap because no-one will want to travel up there twice a day!"