Not entirely true, but you're right, this isn't a good case for retrofits, at least not unless you're going back to the studs. Not disagreeing with you at all on that point, but if anyone else is still following this thread that I've so ruthlessly hijacked, (sorry, folks!), hopefully the below is of interest.
In commercial environments, we deploy IEEE 802.3bt Type 4 POE and Cisco's enhanced version of that called UPOE+ at 90W on low-voltage CAT6 cabling. You can daisy-chain PoE LEDs or use PoE pass-through to extend the reach of single runs. For example, Igor's typical office ceiling luminaire is 20W, meaning you can easily power 3 of them daisy-chained together, plus additional lower-power devices like occupancy and temperature sensors, (typically 5V USB), door badge readers and locks, and so on with a single run. For home fixtures that only draw say, 5W, you could easily support 15 pot lights on a single run. Sadly, I have not seen pot lights with daisy-chaining capabilities emerge on the market yet. (Igor may have an applicable patent that holds that up due to licensing/royalties, but I'm not certain.)
You can even go beyond PoE with DC cabling for power distribution with solutions from companies like VoltServer. Their product is IEC 62368-1 LPS approved for sending 1kW over a single copper pair up to 2km. Using that, you can centralize power for entire PoE switches, remote UPS, and all sorts of applications.
Sure, it requires non-standard cabling rather than good ol' CAT6, (18 to 12 AWG pairs vs. 23 AWG in CAT6), but it's available from any Belden supplier or similar. I haven't had a project to work with this yet, but it's very cost-efficient, in terms of both installation and operations, since you don't need to run the cable in conduit and--like PoE--you don't really even need an electrician. AND it's safe to touch--power is cut off within 3ms of an abnormal condition. This may not fall under NEC Class 2, but it's been deployed in hotels, schools, and hospitals, so you know it's approved.
Check out this article from a few years ago when they were still considered a start-up: VoltServer Solution Provides Power That Is Safe To Touch.