Make the whole building mixed-use. Ring the outside with apartments, and keep the inside commercial. Make the whole thing a little community in itself.
Just fill the whole center of it with cafés, bodegas, computer repair shops—the kinds of small, locally-owned shops you get in a (healthy) small town or a pre-modern-zoning city area.
The plumbing remains a major problem, however. Restrooms and other plumbing are very centrally located in an office tower and the newer and more modern that office tower is the more central and consolidated they are.
Anything is possible, of course, but solving the light issue is just one item… The plumbing issue is at least as complicated.
The biggest challenge I see is in how to segregate commercial and residential traffic. Residents will not mostly want to live somewhere that they encounter random strangers walking through their hallways all the time. A purpose-built residential tower can limit access per floor fairly easily. In low-rise buildings with living area above retail, you segregate at the door to the upper floors.
Cyberpunk 2077, here we come!
You would have to design these weird apartments though that are like a thinly sliced pizza with no central area. Just a long hall of connecting rooms.
Or to retro fit all you have is the foundation and sides, everything else is basically wrong and cost wise you have less than nothing. It is just cheaper to start over and not have to undo all the wrong aspects.
We are mostly in denial in the US that there is going to be a ton of empty, useless buildings along with many regional banks going out of business.
Those used to be called "shotgun houses" (or, less euphemistically, "shotgun shacks") though they were rectangular, not pizza-shaped.
https://en.wikipedia.org/wiki/Shotgun_house
Of course, people did live in them because they were cheap.
In overpriced urban areas, the "pizza slice" configuration might be tolerable to some, if it were cheap enough.
That’s not the case everywhere. In ‘Europe’ (I don’t know what set of countries this applies to), workers must be able to get sufficient natural daylight.
https://www.kingspan.com/ie/en/knowledge-articles/what-is-en...:
“To comply with the minimum recommendations for indoor spaces lit with windows or curtain walling, over 50% of the space must achieve 300 lux for more than half the daylight hours in the year. In addition, to prevent particularly gloomy areas being created within a room, a backstop value of 100 lux has to be met across the entire space for the same period.
If rooflights are used to provide daylight into the space, then the requirements are more demanding with a value of 300 lux required for the whole of the relevant space for at least half of the daylight hours.”
Office buildings floor plates and residential floor plates aren't really compatable.
Office buildings have most of their floor plates not around windows, where are residential needs some light.
Also water, and sewer need to be retrofitted.
The one building that was a successful conversion that I know of cut out the center of the building to create a light corridor down the center of the building.
The Odd lots podcast had a recent episode on this and the guest said that converting office to residential is often more expensive than rebuilding.
So you've got a good though but its rarely practical in the larger city style office buildings.
Perhaps smaller density 6 story buildings would be easier to do?