After switching to nodejs v4.2.5 by:
nvm install v4.2.5 nvm use v4.2.5 curl -L https://npmjs.org/install.sh | sh
and re-installing all dependencies via npm install, the osm-bright-fonts was placed in the ./node_modules dir instead of ./node_modules/osm-bright-style/node_modules as before. Apparently npm install places everything in the same root node_modules dir (possibly unless it runs into a conflict). This resulted in kartotherian not working because osm-bright-style uses a hardcoded sub-path for fonts instead of using node's require().
We need to figure out how to either force osm-bright-fonts to always be placed into the predefined subdir by npm install, or to dynamically update all these paths: