The problem is that fonts are icons, in that they are arbitrary collections of curves, shapes, and symbols, which communicate meaning only to the end-user, and are highly dependent on the end-users understanding of what the thing is that they are clicking, will do.
An icon, a font symbol, a glpyh, a ligature - these are all mere lines in the sand. You want to make another file-format with that, kid?
You can use whatever curve, shape and symbol you like, but the unicode U+0079 should essentially represent the letter 'y' (rather than 'umbrella'): that's precisely the point of it.
If I don't get your symbol, I should be able to revert to a font that I do get.
Symbols are random things that mean nothing until someone says it. If you and I agree that U+0079 is 'y', then so be it. But lets use the other namespaces of the index, too .. and in that regard .ttf has much to offer the aspiring user of the format. Problem is, a shallow look at it, of course, renders the conclusion that it is an investment; but if I know for sure my glyphs render the same way for grandma, no matter if she's using it on some grungy screen, somewhere, then I'm okay with letting the heart-beat monitor screen be composed mostly of cache-able sub-functions derived from somewhere_safe.ttf.
On the other hand, using SVG to pre-load values, then modifying the decomposed stack, somewhere appropriate, in order to attain sustainable realtime SVG rendering performance .. seems as if its a matter of principle. Could it be the jury is out until someone says screw it, and bases the entire OS of their new device on SVG, alone, and not much else?
I think the recent xkcd about symbols is very relevant here, interestingly. As more and more folks were having fun with icons, whether fonts or otherwise, to represent things, it is hilarious how many more slight variations of a symbol I had to learn. Only to usually have sites revert back to using the words at some point.
That is, arguing that symbols are random seems silly. The whole point is that there is a large base of agreed upon symbols affixed with meanings already. They can even be combined to form different already agreed upon symbols.
Ok, allow me to rephrase. Fonts shouldn't be used as icons in such a way that the same point gives me a wholly different icon in a different font. A 'y' will look like a 'y' in any reasonable font. Github's settings icon just looks like a broken box in most other fonts () and if it doesn't, then you're still not sure it resembles something that would, in some way, remind you of "settings".
I know and because of this something nice looking in one font becomes something completely useless when not using that font. (like the Github character in my previous post) It's exactly what I dislike about the entire practice. I don't want to have to use a certain font to make sure your site doesn't break.
I like the consistency of having the same fonts that I like and find readable in my browser as I have in every other window on my computer. Browsers give me the chance to aim for that consistency by picking one font for all sites, but then some sites look terrible because they rely on some particular font to show non standardized icons.
You seem to be confusing fonts with letters or characters (graphemes). A font is simply a collection of specific visual representations of graphemes, each of which should be readily understandable by any reader as a representation of a certain grapheme. An icon, on the other hand, has no strict tie to a grapheme (some might happen to be graphemes, but most aren't). Of course, Unicode, in all its vastness and splendor, has chosen to include lots of code points that wouldn't traditionally be considered graphemes, and fonts are expected to contain specific visual representations for those as well. So at the end of the day things are complicated.
The problem is that fonts are icons, in that they are arbitrary collections of curves, shapes, and symbols, which communicate meaning only to the end-user, and are highly dependent on the end-users understanding of what the thing is that they are clicking, will do.
An icon, a font symbol, a glpyh, a ligature - these are all mere lines in the sand. You want to make another file-format with that, kid?