This was discussed at today's fesco during open floor. Opening a ticket with the background and decision in case someone needs to reference it later.

nodejs is a framework for running javascript on a host instead of inside a web browser. Upstream's code installs and searches for libraries written for nodejs underneath /usr/lib. Nodejs is not multilib aware in that we cannot install nodejs.x86 and nodejs.x86_64 on one host and expect something functional to come out of it.

Libraries written for nodejs can both be pure javascript and compiled extensions. The compiled extensions are arch-specific. In order to use the /usr/lib directory for these, FESCo would need to grant a multilib exemption. Both the nodejs package maintainers and the FPC think that this is appropriate in this case. The case is very similar to the Java multilib exemption granted a few weeks ago.