Yes - when the first wave of emails hit EU users several months ago, I complained on HN that I'd be fine with paying for GandiMail as long as I had 6 months notice or whatever.
The email I got today was pretty clear and no-BS, it says flat out that pricing changes are effective in 30 days for "all our existing services and the new Mailbox service" - price hikes aren't exactly fun, but my domain is registered out for a few years already and I'm using their email service for free... so is 30-day notice of a pricing increase _truly_ only 30 days notice? Not really, not for a vendor whom I only pay annually in advance.
Notably the existing, free GandiMail service stays up until November which is the part I was worried about. So this seems fine to me, I am happy to become a paying customer for email and they've made this easy by giving me plenty of time to onboard. Domain registry fees are already cheap, I don't really care about paying a little more to keep my domain. For my TLD it looks like prices are going up the equivalent of 60 cents per month.
I have been freeloading on GandiMail for several years and it's been great. I am happy to pay $4/mo for a standard inbox (at least while I shop around) especially if they are upgrading their product. Currently GandiMail's MFA scheme is pretty crappy/broken so I am excited to see what I'll be able to get in return for my money after they complete their changes.