I'm pretty sure one of the first app stores we'll see is Meta App Store.
The deliberate delay in releasing the Threads app in the EU, without any clear reason, makes me believe that they intend to make it an exclusive offering of the Meta store.
With Encrypted Client Hello being rolled out (default on Firefox, optional on chrome/edge with Cloudflare DNS). ISPs can't technically block any website anymore.
They used to block DNS requests, then when secure DNS rolled out, they targeted SNI requests.
But with ECH there is nothing to block except the ip address, which is dynamic and doesn't even belong to the website if it was hosted on a CDN.