Fact is that while yes, Toyota is being proactive, they had better be. Toyota has a reputation on the line, and this is an issue that most would have thought to have disappeared in the '80's. No company wants to pay hours worth of labour and tie up bay areas for thousands upon thousands of Echos if there wasn't a significant issue. Rust eating out the floor board prematurely IS a significant issue, but if taken care of I'm sure won't turn into a PR fiasco.
Mazda is the model company for me where the customer is taken care of due to warranty issues. They've shown that decades ago when they bought-back all those rotaries, again with the overstated hp (offering free accessories, service dollars, or repurchase), and on the Mazda5 (free loaner for 5-6 weeks, restarting of the warranty period, AND dollars). That said, echoing others (pun intended), the domestics mostly likely wouldn't have stepped up to the plate to recall this issue - they'd instead consider the cost and weigh it against potential lawsuit damages.
In any case, could this be a case of the EH not being 'designed' for Canadian climate? Maybe, maybe not. Sedans are affected too. Man do cars ever look scary when the entire interior is disassembled for something like this. I wouldn't want to be the tech, or get someone on a bad day doing a rush job!