Yes, they should, because I _need_ good feedback for connection issues.
I have not used those two specific apps, but for other "online first" apps it's such a common problem. Open an app, type a note, switch back to a different app (or turn off your phone, or close laptop lid).
Later on, you want to access the note and it's not there. Why? the authors decided to be "smart" and "offline first" and made sync in background, with no feedback, or with heavily delayed feedback... and I was walking out of wifi range when i was typing the note, so connection was spotty.
The OP's demo TODO app has exactly the same problem - no indication when the data is already uploaded. So please, if your real goal is collaboration, let user know when you cannot perform it, don't sweep it under the rug hoping the things would get uploaded eventually.
In regard to the TODO demo - I should totally add that. Thanks :) https://github.com/orbitinghail/sqlsync/issues/31
I think my sibling comments are completely underestimating the complexity and the market value here. Apple Reminders or Google Tasks are customer facing applications for single individuals, nobody but a single client is working at a time on their own data. Businesses on the other hand want their data at a central location and personnel close to the tasks using client applications. They don't want any reliability issues in the client-server-communication blocking the work being done. Heck, businesses want to be able to throw more people at the same tasks and we call it collaborative editing.
That would allow offline viewing to a variety of apps, regardless of approach.
Last time I checked Google Docs doesn't primarily allow editing offline files, which hints how hard it is to support substantial features beyond mere reading.
I just don't think there are "embarrassingly client-side, but also needs a server for some reason" web apps that would benefit from this in the real world. Even Google's or Apple's version of the simple Todo app has a lot of (useful) integrations, which means having some level of trust with the client.