Daniel Glazman writes, somewhat in passing:
We can now apply SVG filters to all content, including HTML 4, in Firefox but I have mixed feelings about the fact you have to know HTML, CSS and SVG to apply such a filter. Seems to me overkill, and too far away from the original spirit of the Web.
He didn't enable comments on that post, so I'll reply here: you don't need to know SVG to use filters. You can just paste filter code from a cookbook into an XML file --- or use an XML file from a library --- and refer to that file from your CSS and HTML. This is not only easy and reasonable; SVG filters provide a rich vocabulary of composable operators, so they're much more flexible and powerful than providing ten canned filter keywords to handle all the author needs that the CSS WG can think of.
You could perhaps reinvent SVG filters with CSS syntax, but I don't see that as a real win for author understanding.
Generally in computer science we prefer to create a set of composable primitives with clean semantics, on top of which libraries are built to make frequent tasks easy, over trying to anticipate every possible need and encoding a feature for each one. Unfortunately CSS has often taken the latter course ... partly because the Web's mechanisms for code reuse are weak. But external document references give us a reuse mechanism that makes using a library of SVG effects quite convenient, IMHO.