Another annoying reseating datapoint (of which there have to be a dwindling number, hopefully...) which didn't happen to me, but thought I'd report:

E35K status books YYZ-YVR for this weekend a few months ago, and bought 18J and 18K. Seat map at time of booking showed pre-densification configuration.

In the mean time, 777s are refurbed and the one servicing this mission is switched out to a refurbished plane. Of course, none of the passengers are alerted to this or given the opportunity to revisit their (paid) seat selections.

Come check in, somehow the Air Canada IT gods have decided that the best resolution is to leave one passenger in 18K but move one passenger to 12E. How this could have possibly made sense is beyond me.

Cue the call-in (T-20hrs or so). Resolution that is offered: move both passengers to the middle two seats of the middle section of Row 30 (excellent! Now both passengers can share in the joy of being a middle seat on the HD). No refunds available -- the best the agent could do was say "contact customer service and let them know you would like a refund." No room in the PE cabin, no more seats by the window.

Obviously with the 777 refurbs nearly complete, AC can now be upfront and honest in selling people crappy densified seats, rather than advertising/selling less-crappy undensified seats and then switching passengers out as quietly as possible into crappy densified seats as the new HDs come in service. But even if you're gonna do the annoying bait and switch, the best approach cannot possibly be splitting up passengers who are travelling together on the same reservation on paid/selected seats. Dumb dumb dumb.