Sounds interesting. Our internal elevation service is built upon multiple services where it tries to use (what we believe to be) the best one first, if that doesn't have data, fallback to the next one and so on. Also based on bounding boxes of course. This makes it fairly easy to add new data sources.
I started to look at Sweden's data. It's linked from here:
https://www.lantmateriet.se/sv/Kartor-och-geografisk-information/oppna-data/ . Fetched from the "Hämta via FTP", an account is needed though. But there is also a Language-select top left.
Sweden has two data-sets, they are described at
https://www.lantmateriet.se/sv/Kartor-och-geografisk-information/oppna-data/#faq=b47b
The article at rapidlasso.com says there are 1-2 measurements per m2, as I understand it. But the FAQ I linked says that the data only has one measure point per 50 meters, which is only slightly better than SRTM90. However, the data itself might very well be better.
The data at Lantmäteriet is in geotiff. I don't have a generic geotiff reader in hand, so I would have to write that (and learn the format). It doesn't seem like the most advanced task though.
As you can imagine I understood less of the Sachsen data.
The biggest problem in my opinion though is that this would end up with many many different sources that should be updated regularly. Probably with different code for each country as well. It's not very smooth.
