I think we should challenge the "need" to embed a font at all. At the present state of the art, offering a client a facsimile of a printed book (though this is so often what the client WANTS) is doomed to failure. We should also challenge the conventional workflow of importing to Word, then to HTML, then to Sigil. If Sigil starts with clean text, it's very easy to add as much formatting as an eBook can realistically take, and still be portable.
I spend too much time tarting up code so a client sees "perfection" on their favourite device, knowing quite well that details of layout will be different on others but keeping my mouth shut!