> Well, the other option is to remove it, and then add it back once
> somebody complains - which is unlikely to happen. The clock parameter
> is PCF8584 specific anyway, and  I think removing it is a good option,

My suggestion is to do that incrementally. First, get your driver
accepted. Second, do the cleanups which affect elektor as well later.

> as I've done the same with getown() (where in i2c-elektor, 'own' sets
> the PCF8584's own address).

I wondered about that. Can the PCF8584 really act as a slave, too?
Somewhen I need to check its datasheet.

> Question is, if I remove the parameter, I'd like it to be
> non-destructive. Do you know of anything that can go wrong if the I2C
> master is running the bus on a wrong clock?

Not sure if I understand you correctly, but if the bus freq is too fast
then devices won't respond. Too slow is not a problem.