I can only speak for myself here of course, but it doesn’t matter to me if an app is open or closed source. What matters is having a nice experience. I am currently very happy with Liftoff and I didn’t even know it was open source.

If another app comes along with new or better features, I will try it out and maybe even switch, regardless of whether it is closed or open source. And if they have an attractive pay model for interesting features, why not?

We need to see how it all plays out. What about the Lemmy instances themselves? Especially the larger ones need to make money too. Can they survive solely on donations like Wikipedia, or do they have to run ads at some point in the future?

That should be on case in all of Europe (in Germany and Italy for sure). It’s covered but your insurance as long as there is an emergency. So you can’t just use the ambulance as a taxi, then you would be billed the whole amount.