I don't know any airline that offers an unlimited weight (or volume) of carry-on luggage.

You can be sure that, when the baggage charges come in next week, that there will be a whole lot more hand luggage attempted to be brought on board - so you can expect KLM to similarly increase their checks on carry-on baggage.

I already find KLM to be one of the airlines most concerned with carry-on luggage. If ever I check a bag, they nearly always also inquire about my carry-on, and ask to see it. If I'm checking a bag, I usually only have a small bag to bring on board, which never then merits further attention - but sometimes they will insist on attaching the yellow "Cabin Approved" sticker, and most of the bags I see coming on board have this yellow sticker on.

Often there are rigmaroles at boarding, too, with people being told their bags will have to be checked, or further rigmaroles on board full flights with people coming forward from the back and asking the staff to put their bag "in the wardrobe" (which won't be around for much longer!!!)

I would expect that anyone that does not have the yellow "Cabin Approved" sticker by the time they get to the gate will face even tougher scrutiny from now on - and even that sticker may not be guarantee enough to prevent it being gate checked!!!