What's the software? Google CalDAV support isn't actually going away, it's just switching to a whitelist, so depending on your client, it should be fine. I don't know how that's going to work exactly (is it just an API key? how will that work with open source calendaring software like Lightning?), but if it's even moderately actively maintained software, it's likely that they've already applied for access.
> Google started by dropping XMPP invites under the questionable guise of spam protection (from the article)
Just FYI, they turned federation back on shortly afterwards. Of course, it's being dropped for the new chat system, but it's worth getting that right.
> Fastmail is owned by Opera Software and operates both free and paid tiers of service
As others have pointed out, there is no free tier, just a free trial. And if you're going to pay for it, I don't really see the difference between that and going full Google Apps, but that's just me. (edit: ah, apparently there used to be a free tier, but no longer)
Regardless, paying for the services you use is a good thing, both for getting better guarantees for service, and for teaching the market that ad-supported services aren't the end-all be-all, that we can have other business models, and maybe even a diverse market of them to support different uses and different requirements.