Oliver here from the Memex team.

Thanks for adding so much input to the conversation. :)

Let me address a few points you made:

> A complete P2P system would upend that model, assuming it could be made to work well (the asymmetry of the broadband infrastructure for consumers doesn't help, either).

There have been a few decisions we had to make in the past in order to provide a non-technical user friendly, scalable, affordable and privacy focused product.

One option would be to use newer p2p technologies like IPFS(https://github.com/ipfs/) or Dat(http://datproject.org). Those would provide high decentralisation but have a couple of drawbacks that make it not suitable for our use case. Indeed they are difficult to make work well.
1) The technologies are not ready yet. They all still have significant performance and scalability issues which won't be solved in the next 1-2 years (optimistically)
2) They are unsuitable for private data as they shard your very personal knowledge across nodes you don't know. At least that is how they now work. Private networks are planned but it is still a far way to go.
3) They are not suitable for non-technical users yet

Next option are blockchains. Let's not talk about that :P But seriously who wants to store their personal data like a history on an immutable ledger. Nope not gonna happen.

Next option is using a p2p sync via WebRTC, which we actually do use. Our servers are only there to offer a relay service to pass your message for asynchronous syncing and signalling for synchronous syncing and to punch through your firewalls. The sync messages are end2end encrypted and deleted from our servers when all devices have picked up the message. This approach offers the ability to be much cheaper than whats out there because we don't have to store the data on a cloud constantly.

> Today's system takes control away from the users for the most part, unless they pay extra (ie - to create and maintain a server or whatnot for their own personal content - or not pay, or not pay by giving away other information that the company giving them "free hosting" or whatnot can use).

For both p2p or cloud infrastructure, you won't get around servers. Someone needs to pay for that too. (and we are not even including the development costs for the software).
Even if you would use a full p2p system like IPFS and dat, once they become more common there is a need for infrastructure someone maintains. It's probably your ISP that then starts charging more. There is no free lunch.
In the end it begs the question if it it so bad that you have to pay a bit for services that really make your life better? I don't think thats a bad thing. We got so used to getting things for free without valuing how they contribute to our lives.
Except of course you give away your data, in return for those free services in (implicit) exchange for data, which is not an option for us. We won't rule out that there might be a very consensual relationship between users and us to share data and do some amazing stuff with it, but also let them participate in the fruits. But that is definitely not the default like on most other services. By default your data is always yours.

In our case we will initially offer the syncing service for a premium subscription. The code is all there though, so it can be made self hostable. We either need a committed group of contributors taking this in their hands, or need to make the money first to have the capacity to do that. Either way it's unlikely going to happen immediately, but we definitely want to see it.

> (this seems to be a siloed system, if anything).

However most importantly is to express one of our core values: We think optimising for interoperability is far far more important than decentralisation. We believe if users have the ability to easily move between different providers/silos of a software and take their data and social graph with them a lot of the trust issue we experience today, and hope decentralisation helps, would be solved.
If users can migrate to more ethical and privacy focused services easily, it would put an incentive on ethical and trustworthy behaviour and would be able to still use the many advantages of centralised systems (iteration speed, cost efficiency, development convenience, performance).

To protect your privacy, data ownership and freedom to move, we already invested considerable effort.

1) We focus on the software being offline first. This had quite some challenges, among others to get search and storage performant enough in the browser.

2) We build a database and storage layer that will turn into an interoperable datastore for knowledge data that gives you full control over your data (https://github.com/worldbrain/storex). Memex will turn into a light client so you can copy/fork it, adapt it to your needs and use the same database. So you don't even have to migrate anymore.

3) We have a completely different approach to set the economic incentives in our company. We don't raise venture capital so 1) we don't create incentives to lock you into our service and 2) provide you free services that exploit your privacy for the sake of growth:
To raise capital we use a model called Steward Ownership, that aligns with the incentives for interoperability. We did that because we believe there needs to be an ecosystem of many "memex"-like tools developed by other people that interoperably work together. More you can read here: https://community.worldbrain.io/t/why-worldbrain-io-does-not...
It took us almost 2 years to find money from investors because not taking venture capital was so fundamentally important for our vision. So we had to refuse a lot: https://community.worldbrain.io/t/how-worldbrain-io-tries-to...

I hope that answers many of your questions, and likely spurs many more. Happy to answer them :)