The main ones are that certain users or groups of users end up dominating each community, and that mods become abusive over time. Brigading and bigotry are big issues too. You also mentioned echo chambers, which I agree is another issue, although that is present in many social media platforms.
Unfortunately, federation doesn't solve these issues. At the very least, some kind of basic improvements are needed. Ideas like preventing large communities from dominating the front page, removing or limiting the effect of downvotes, or having more checks and balances for what mods can do, are necessary. But none of that happened. So this attempt at a Reddit clone is just ending up as a bad Reddit clone. Which is probably why Lemmy/Kbin/Mbin will slowly fade away, once people realize that it is just a Reddit clone.
This won't be the final attempt at creating a replacement for Reddit. Eventually, enshittification will destroy Reddit, and something else will replace it. But it probably won't be the Fediverse's attempt at it.
So many instances block Hexbear and others. We are well on the path of creating separated communities, just with the added headache of having to police federation. Not to mention the problem of power users and out-of-control mods, which federation makes worse rather than solving them.
Ultimately, I think a real Reddit replacement will have to think hard about fixing the fundamental problems of this form of social media, rather than attempting to use buzzwords or cool new ideas.
Federation makes sense for a Twitter replacement. Not so much for a Reddit replacement. I get the feeling that we are at an end to the experiment. Eventually, people will realize that we cannot replace Reddit with a Fediverse based solution.
My recent realization is that the very high-end of the GPU market is totally unnecessary. A 4070 can play practically any game at 4K with decent framerates. And if you are fine with just "high" settings instead of maxed out, at very good framerates too.
Fuel cells have the potential to help overcome the challenges associated with Battery Electric Vehicles (BEV), namely a dependency on limited natural resources, electric grid capacity, battery charging time and vehicle range. Fuel cells can also be as cheap to manufacture as internal combustion engines and can be produced using recycled and recyclable materials.
Reminder that fuel cells are less dependent on resources than batteries, can be about as cheap as ICEs to make, and can be made out of recycled materials.
Then you are creating an imaginary set of problems for hydrogen. We already have hydrogen cars that can go 400 miles. The range problem is already a solved problem. Future innovations will improve this even further. We already have hydrogen drones and bikes too. So there is no problem scaling down. Not to mention SUVs make up nearly 80% of the market these days. You're basically inverting how the real world car market works.
As we run into the fundamental problems of batteries, such as needing charging stations everywhere, and very high powered ones if we want fast charging, it will eventually become obvious that no amount of advancements will solve some of those issues. We will want to look at alternative solutions.
And again, BEVs are not competitive right now. They are a artificial market propped up by governments around the world. ICE cars still rule the world. And likely BEVs will retreat in the market as subsidy reductions and trade wars make them even less uncompetitive.
Hydrogen got a tiny fraction of the subsidies that batteries got. We probably looking at well beyond $1 trillion for the latter, if you include everything, such as all the subsidies and government loans from China. If were serious about making hydrogen a thing, we would've increase subsidies by a factor of something like 100x.
Battery cars have not "won." In fact, they are barely alive as a self-sustaining industry. ICE cars still dominate, and if anything they are gaining ground with blended solutions like hybrids or PHEVs. This is what I mean by "drinking the kool-aid." BEV fans are making claims that fly in the face of reality. And it's more than likely that if we take away the subsidies, the BEV industry would quickly collapse and shrink to a tiny niche.
The problem is that BEVs only really make sense as urban commuters for people with garages, and smaller ideas like e-scooters or e-bikes. It's not really something that make sense for larger vehicles or long-distance vehicles. And trying to force the issue just means a lot of SUV sized BEVs, which are definitely not a solution to anything. By admitting they're not perfect is admitting we should scale back BEV subsidies and start seriously promoting alternatives.