As mentioned below I have been building the 'read' side of this: a data publication platform. I wanted to avoid any server side components. The communication / write part and updating the server-side sqlite database would need running components on the server which I wanted to avoid.
The 'write' part would technically be very doable and not that different from other back-ends.
Looks like a good addition to the datasette ecosystem. I have been working on a similar idea with cusom html around sqlite databases. By default a faceted search interface is generated but by reusing the client side data layer, custom apps are made easy.
The design keeps data and presentation together and even maps do not rely on external services.
A bit of fun I had last night with running a HTTP request through a stupid amount of proxies. The main take-away is that a http proxy will not add too much latency, assuming fast interconnects. I would, however, not advise to chain 500 proxies.
Perhaps also of interest: A more curated example of a local initiative can be found here: https://kaart.gentgemapt.be/. This combines historical maps of a city in Belgium with information on local heritage.