How suitable are GaN half-bridges for small brushless motor drives (ESCs)?
Of course much of this depends on the system requirements, switching speed, cost goals, performance requirements.
The main challenge is there are no P-Channel GAN FETs available as far as I know.  So you would need some way to drive the high side N-FETs even if you could drive the low side directly and were operating the bridge at 5V.
GAN gate drive requirements are tricky- Exceeding the max specified gate voltage even during transients or ringing can destroy the device.
GAN is also still much more expensive than silicon, and there are no integrated 3 phase GAN bridges like the ones you can find in silicon.  There are integrated driver + GAN fet half bridge parts however, like this one from TI.