It really depends on the local Authority, I would say the most common is 48hours, but there are also lots of unlimited ones. Normally people who want long term will go to campsites some of which will offer some really cheap off-season deals but there are of course people who over stay on aires and abuse them, there was a guy on the Biarritz one for years and gradually there was a van and I think even a bit of a shed, it was a right mess. He was supposed to be a guy who the mayor had taken pity on because he had nowhere to go but he soon found somewhere else when the barriers were installed!Will there be limits on the duration of stay and will the Germans, Dutch etc turn them into long-term campsites? I'm guessing they're taking the French model to generate more income for local communities and giving alternatives to increasingly illegal wild camps. How would they benefit UK motorhomers 90/180?
AFAICS the biggest impact on your plans will be a bit more planning, the main people who will be affected by this are the ones that drive to Benidorm/ benicassim etc and stay for the whole winter, We prefer touring so don't tend to want to stay so long in one place, so we were already planning to go to Morocco more ( Morocco is big we did 2000 miles in 2019, 4th trip and still havent seen it all) and I'm thinking Balkans and maybe Turkey.