That's great, but I just came back to make an important bit of information more clear :): I need tristate. When The pullup is switched off, it is not supposed to sink several amps, but to be off, that is, gone or high impedance.
I almost thought the NTB0101 would be great, but the auto-directionsensing is undefined in case another (strong) pullup is in the network, so that in the worst case, the network is sensed as an input and the MCU direction as an output, leading essentially to a short-circuit.
Since it is not completely unrealistic (I found almost suitable buffers that only failed V_HI), it would also be great if I could use the same chip at another place, where I have to translate 5V to 3.3V (bi-state, sensing on the trigger line) to keep the BOM down.