I wasn't meaning to criticise KLM multi-city booking tool, and indeed, I generally find it better than the booking tools on the other airlines websites that I frequent (which admittedly does not include BA). KLM also has the "return from/to a different destination" option, which is very useful for booking open-jaws, with the normal range of fare-class options (although it doesn't help with stop-overs).

However, in terms of future improvements to the multi-city tool, better fare-class selection would certainly be something I'd be interested to see.