The reverse breakdown voltage of the BE junction of a transistor is usually somewhere near 5 volts. It never goes to 10 volts - maybe in some very special cases.

This makes this circuit unusable above 8 volt logic "levels".

I also suspect it will give a huge overshoot into the 3 volt circuitry on the rising edge of the 5 volt side. In the worst case it will bite the circuitry in there.

Bipolar transistors are also performing badly when driven to saturation. Looks like they have mentioned that in the article but this also affects a bundle of parameters which in turn cause instability etc. I think someone mentioned this already.

Bidirectional level shifting - I personally avoid it if possible. It is a very complex thing to do even with readily available circuits and the complexity is not the number of pins it is the initialization and especially the circumstances BEFORE initialization has taken place.