It’s soon OK to link to stylesheets directly from anywhere inside the <body> without having FOUCs:
The plan is for each
<link rel="stylesheet">to block rendering of subsequent content while the stylesheet loads, but allow the rendering of content before it. The stylesheets load in parallel, but they apply in series. This makes<link rel="stylesheet">behave similar to<script src="…"></script>.
A use case could be for taking a component based approach, each with its own CSS file that you load up just before you actually use it.
Already works nice in IE/Edge, and Firefox (with a little fix). The proposed behaviour is planned to land in Chromium.