WS2812: I've certainly thought about them, but:
A) You need RGBW, not just RGB. There are SK6812-based addressable RGBW strips, but they're substantially more expensive ($10/meter vs $4.5/meter), so even adding in the cost of a separate driver means the RGBW strips are cheaper.
B) I don't quite think you've contemplated the scale of this project. It'd involve 300 meters of LED strip, and 18 000 LEDs. You'd still need drivers for every single piece of WS2812 strip, because daisy-chaining several thousand is not going to work. Also, there is zero gain in using addressable LEDs, as you'd always be setting a whole set of 120 LEDs to the same value anyway.
C) They run on 5V. This means wiring costs would explode (you need 5x as much copper - and the whole mess would reach something on the order of 1100 amps peak), plus there will be way stronger brightness changes across a strip.
D) They only offer 256 levels. That may sound like a lot, but you will lose all control at lower dimming levels, since under normal operation the tiles will only run at 10-15% power.
As for buying WS2811 driver chips: Since these are constant current devices, you can't really use them to drive whole strips. They just don't offer enough current capacity, and you can't easily extend it. And even if you did... well, they're still $0.13/pop, vs the $0.74/pop PIC micros (and you'd need output transistors in either case). Not a massive saving; even if it worked, it'd be on the order of $100.
It's entirely reasonable for a smaller project, but by the end of the day, you'd end up wasting well over $1000 by going for addressable strips.