it's easy enough to edit web fonts to include only necessary characters, but most EULAs won't allow for this. any font licensed under the SIL open font license is fine, though you may have to change the font's name if it has a reserved font name (check the license file). this makes a
huge difference (fonts under 10k), but no one ever bothers to do it. not sure if inlining them as base64 in your CSS and serving with gzip would help much more.
a lot of the stuff that we do in font editors is going to start happening in-browser. variable fonts that use two masters (the thinnest and heaviest font weights) to interpolate all the other weights in-browser are an emerging standard that will get font sizes down[0]. you're essentially being sent two fonts over the wire that can generate quite a few more. font files are bloated in a number of ways. eventually we'll have a standard where diacritics like ¨´ etc can automatically be added to letters without the need for an entirely separate glyph. (å,a,á,ä, are currently separate, which is very expensive).
google, adobe, and other big players are hard at work on this stuff, and it won't be long. there are pain points now, for sure, but to me this isn't an argument in favor of system fonts. most of web design is typography design, and anyone who says otherwise probably hasn't been designing for the web very long.
0. http://blog.typekit.com/2016/09/14/variable-fonts-a-new-kind...