Disagree. It’s a poor hack and therefore nothing we should want in a professional framework for thousands of websites. You trick the browser into thinking the fonts are not used for screen at all, then after the page is loaded, you say “April fools! Now switch to the webfont!”. It creates a terrible user experience because of the delayed and unreliable font change long after the page started rendering and the “local font first, use webfont later“ is already available as CSS declaration. It works in a much more reliable and optimized way because it was specifically designed for this use.
If loading webfonts is not acceptable in terms of the loading times, the solution is simple: don’t use webfonts, which Invision Community already supports. onLoad is not the right moment to activate webfonts.