I think this could work if it was a kind of demo instance that after some weeks or so would show increasingly annoying popups to switch to another instance.
The official Mastodon app kinda follows that idea with mastodon.social, just that the annoyance isn't intentional but a result of their bad moderation and thus spam problem.
This is not either or. You can store things only until the recipient comes online and then delete it (but Matrix specifically doesn't do this and conceptually can't due to its design).
Well... there has been some recent museings about something like that from the CEO of Element, but it would effectively cause a two class federation where some servers can not work independently of others (likely in reality mainly servers running on EMS infrastructure, a bit like how in Bluesky you can't really work fully independent of their infra, and yes Bluesky was explicitly mentioned as inspiration for that idea).
Having those two options fully independent would basically mean reimplenting xmpp in json as an incompatible alternative protocol and that would make little sense IMHO.
While Synapse isn't great, the problem is that the Matrix protocol is over-designed for a very specific purpose (distributed rooms), that comes with a severe performance penalty but most people don't actually need this for chat.
Its one of these cases of a neat idea on paper, but ultimately a solution looking for a problem.
That said, Matrix isn't that bad overall, but there are better options like XMPP.
There is plenty of "content", it just doesn't get shoved in your face automatically. I personally can't keep up with my non-Lemmy ActivityPub feed and the presenter is absolutely correct about time-zone issues in that regard. The Phanpy catch-up feature that presents your feed more like an email inbox sorted by user account helps with that though.
That said, once you get over FOMO it is really fine and I don't mind getting bored of it at all.
Because of AI bots ignoring robots.txt (especially when you don't explicitly mention their user-agent and rather use a * wildcard) more and more people are implementing exactly that and I wouldn't be surprised if that is what triggered the need to implement robots.txt support for FediDB.
It does via the Nextcloud apps. I also use KaraDAV and am quite happy with it.
If you don't like the somewhat barebones web-ui you can use Filestash instead, the docu explains how to set it up with webdav only and pass through the credentials directly (a bit convoluted at first, but once done it works great).
The typical ratio is 1:9:90, meaning only 10% are actively posting or commenting. The Lemmy numbers fit to that surprisingly well, although you would think a few more lurkers would at least vote sometimes (which Lemmy reports as active in the monthly stats). My guess is that the lurkers don't even bother to sign in.
There is no such thing as a blind relay. There will always be meta-data accumulation at such points in the network.
It is possible to try to minimize the meta-data accumulation and obfuscate it further and there are certainly some interesting theorectical concepts for that in systems like SimpleX, Nostr etc. but in the end most of these are just giving a false sense of security.
In addition many of these systems engage in what I call "trust-washing", i.e. them proudly proclaming: "there is no need to trust us, bro!" When in reality there are multiple points of failure in their pretend to be trustless system that they just chose to ignore or try to distract you from.
And when it comes to the real-world, tried and battle tested system like Tor are where I would put my safety, not some brand new crypto-bro dondogle that is funded by venture capital investors (like SimpleX).
I think this could work if it was a kind of demo instance that after some weeks or so would show increasingly annoying popups to switch to another instance.
The official Mastodon app kinda follows that idea with mastodon.social, just that the annoyance isn't intentional but a result of their bad moderation and thus spam problem.