Firefox makes it look like HTML with pdf.js. Wouldn't it be trivial to make something that puts a PDF through that same filter and saves the results to a file? Or do you mean by default so you can just read it in a browser without PDF support?
For my use case, I use a webclipper to drop a copy of the text as Markdown into Joplin as a personal knowledge base. I can't do this with a PDF. My browser downloads the document by default as a preference for user manuals etc that I would want to keep, but for this kind of content a simple web page would be a better choice.
For other users, PDF is well known for lack of accessibility and I hear that it's a poor choice for screen readers but I have little direct knowledge on that.
I'd rather HTML with named anchors so I can link from documents/pages directly to subsections with hyperlinks. This would make it more useful professionally given it's a document that should be referenced by other works.
sigh, PDF is anything but trivial sadly. It is a horrible creature from the bowels of hell. I do wish there was a web document standard that was printable and also editable without dropping a nuclear bomb