I'm surprised they didn't allow for slave clock stretching when
communicating with a legacy i2c device, it will prohibit use of a rather
large class of devices. :(

Yes, but I3C is push/pull IIRC.

As for interrupts you are always free to wire up an out-of-band
interrupt like before. :)

Yes, my wording was a bit too strong. It is possible, sure. Yet, I
understood that one of the features of I3C is to have in-band interrupt
support. We will see if the demand for backward compatibility or "saving
pins" is higher.