[fra]

> No way to safely bring the bus back to idle from mid-transaction. [...] No safe, universal way to bring the bus from tristate, or low, to pulled-up.

These are great points, and I'll add a note about them in the article. Thanks!

> The protocol is extremely hostile to devices with non-zero latency response. [...]

Technically, this is what clock-stretching is for. In practice, you're right that complex devices implemented proxy registers. I've seen it on DP->MIPI bridges for example.