If you're bouncing audio off walls you may get ambience, but you're not going to get a clean stereo image.
Also, the KEF speakers are hardly world beaters. They have a good reputation as PC speakers, but that's not setting the bar very high.
Professional speaker manufacturers like Genelec use a similar adaptive tuning system, and you can buy a microphone and software add-on to flatten the response of any speaker.
https://www.sonarworks.com/reference
The limitations are well known. The correction curve is level-dependent, because room resonance is a time domain phenomenon created by physical standing waves in a 3D space that includes damping elements, and you can't truly correct it with a frequency domain solution.
You can approximate a time-domain correction with convolution and some assumptions about the room geometry and acoustics, but it's never going to be perfect.
Bottom line: I'm sure the Homepod sounds very nice, and - as usual - it's innovating with technology that's been available elsewhere for a while, and made much easier to use.
But it's not magic, and it's not going to sound hugely better than a much more expensive true stereo system.
Of course that'll do just fine for a lot of buyers.
