Blockchains don't really solve that problem. Scalability is a huge issue, and if you are trying to cram several apps onto the same blockchain they are all going to have scaling issues simultaneously.
It isn't a product maturity thing either. At a theoretical level, we don't know how to make blockchains scale. Every node needs to process every transaction, and we don't know how to get around that.
Would be great to move to a model where the end user can pay for the server time. sandstorm.io was (is) exciting for more than a few reasons. But overall it's still an unsolved problem.
I agree about blockchains, but when talking about P2P solutions in general, many scale way more naturally than centralized services.
When I read on HN the engineering posts from Netflix about the enormous engineering efforts required to make their video service scale, I can't help but think: that's a solved problem, Emule/BitTorrent have been providing good access to video for decades! Of course, there is the "monetization" issues... (but there is also on Netflix, good luck finding non-US or indie content there.) On other side of the spectrum, look at Syncthing vs Dropbox.
The thing about Slack is particularly crazy because even their client does not scale too: it was too slow to be usable daily in my 7-year old computer. A freaking chat app!
Admittedly, I hesitate about whether the best solution of the OSS community is to jump and try to replace all those things. At the same time, the kind of software I enjoy most both developing and using is desktop software. That is kind of software that is uses to empower our creativity. While the proprietary software world moves its engineering power to the cloud, we can still use it to build tools that help people expand their imagination. I am thinking on helping making Gimp and Inkscape and Blender and coding tools all those better, but also making new tools that we have not thought of. I think there is still a lot of potential for exploration, creating new interaction models, etc. in this area that we have not explored yet. Sadly for the libre software world, Apple still gets a lot of developer mindshare in that area too...
The N^2 problem of Bitcoin and Ethereum is solvable through sharding. I agree that on-chain scaling is impossible (and the two projects differ in their taste for decentralization vs scalability at their core), but the build out of workable sharding solutions with reasonable trade-offs and a workable topology are underway by both camps. It's just going to take longer than I think a lot of people who bought in with the pay-per-service use case would prefer.
In the case of chat, I'm convinced that the ability to register data in a shared, immutable store like a blockchain with many stakeholders of disparate interests will be valuable to that end even before microtransactions start being sent with every packet on the internet.
It isn't a product maturity thing either. At a theoretical level, we don't know how to make blockchains scale. Every node needs to process every transaction, and we don't know how to get around that.
Would be great to move to a model where the end user can pay for the server time. sandstorm.io was (is) exciting for more than a few reasons. But overall it's still an unsolved problem.