Hello Joerg,
Well, this is true, but RoHS is not the only case where this is true. How many spectacular failures are to come, due to crappy but cheap components, moving production to China, which causes reliability problems both due to low poduction quality and swamping the world market with counterfeit parts. The latter is for maximizing someone's profit, RoHS at least has a more appealing motive.
I don't think you can safely say "when", "if" is still appropiate. Tin whiskers are far from being understood, it is believed that tin/lead solder is a remedy for them. I agree that RoHS is a large scale experiment, but an experiment with unknown result. With regard to your gas furnace controller: no mission critical system must blow up, just because a solder joint fouled up. Defective solder joints were also a common problem in leaded times :-)
Don't know, most consumer products are nowadays anyway products with a life time of less than a few years. RoHS is mostly directed to this market. Personally I don't think it will change much there. The end user doesn't care whether his/her gadget stopped working because a tin whisker appeared or an undersized and overheated capacitor just shorted out. Finally, I don't think there are many VPs of Quality Control left in the consumer business anyway. Most of it looks as if everything which comes from the assembly line is shipped without even a simple on/off test.
Klaus