I'm not sure who is pushing #GlobalSwitchDay probably won't amount to anything, some of these platforms are certainly not ready a massive migration. The #RedditMigration was rough enough on Lemmy, it actually murdered #Kbin; #loops #PeerTube and #Friendica don't have nearly enough well-maintained instances to support any sort of massive migration. And Signal, well its better than WhatsApp, and its mostly Free Software, but it doesn't really align with all of the others that are, or at least intend to be in the case of Loops, federated services based on ActivityPub.
do you know how long between first release "open sourcing" occured? It looks like the current version of Pixelfed is published under the AGPL which is a strong Free Software licesne that all but requires an online open source development model in additon to protection of the four esssential freedoms.
I don't remember exactly. Maybe a year or so.