It always seemed to me that the benefits of icon fonts would be fleeting. Their popularity has been directly correlated with monochromatic icons being "in-style".
Eventually such fonts will inevitably fall out of style. When that happens, will we be left with a useless ecosystem surrounding a fundamentally inflexible core? Or will font rendering engines have evolved to adapt?
Not to be pedantic, but letterforms are fundamentally chain-able icons and those have been around since written language.
More contemporarily, other marks/icons we now would think of as standard are really icons for language control or words themselves. Typographers have been using monochromatic marks and glyphs since the dawn of the printing press.
Typographical symbols work in part because they exist within a specific problem domain whose practitioners are trained to understand them, and also because the constraints of their native domain privilege function (expressing some directive regarding how a given chunk of text should be typeset) over form (the look and feel of the glyphs themselves). Neither of these properties seems likely to be guaranteed for the much more general domain in which web icons exist.
But the types of icons were talking about here (clock, fork and knife, location marker, star, etc.) do not have such a long history in web design as being monochromatic. It's a fairly recent design trend. A fork and knife icon (used to represent restaurants) could just as easily be a detailed, shaded, multi-colored icon.
> When that happens, will we be left with a useless ecosystem surrounding a fundamentally inflexible core
I'm not sure what you're referring to here. Bootstrap's use of font icons? If font icons ever became an issue, they could easily[1] swapped out of such frameworks.
Also note that font icons are also useful in places that can only display text, but allow for changes in fonts. You can see people make use of such icons for things like (e.g.) displaying the weather in xmobar or dzen.
[1] Might be a bunch of work on the back-end, but I don't see how the interface would change all that much. You get the icons now by just applying a class to an element, just the behind-the-scenes CSS would have to change.
Eventually such fonts will inevitably fall out of style. When that happens, will we be left with a useless ecosystem surrounding a fundamentally inflexible core? Or will font rendering engines have evolved to adapt?