~ New Framework
This is taken out of another article. Just moved to its own small post rather than inside that article.
I also followed this CommitStrip comic, I have a cool idea for a framework though.
First let me say this problem can be fixed server side for sure. Just like HTML templates exist there for MVC frameworks you can include and load and do things there that will substitute the need for the rel=import, however that implies you need an application server again to support this. I think it is stronger to have the browser be able to do this. Therefore, I propose the following.
Have an entrypoint in a normal <script> tag that sets some data. Or load it in an index.mjs, just one entrypoint. The entrypoint will use a single method of the framework feeding a config object that will download the html files and inject them into the page. Setting up all the Custom Elements for you, bringing the rel=import back into the browser.