i'm not sure how much of an influencing factor it was to the project as a whole, but from my own experience I think their choice of using RoR prevented a lot of developers from joining in.
Node didn't even exist when they started out. At least not in anything which resembled production quality.
And trying to "install" node on Ubuntu or other Debian-based distros for a long time required getting entire Chrome/V8 to build, from source. Something which was near impossible to setup, unless extremely dedicated.
I tried twice and failed.
Your "npm install diaspora" came with a 20page+ distro-wrecking set of instructions for configuring your build-machine. And if you failed, you woiuld probably have to re-install your distro because of the mess you made.
Those "horrible instructions" listed there look extremely friendly in comparison. They may have done lots of things wrong, but chosing RoR over Node was not one of them.
just that their choice of tech did create a barrier to entry. they could have used something like php if they wanted to make it easy for people to get on board and dev.
compare this: npm install diaspora
to this: https://wiki.diasporafoundation.org/Installation/Ubuntu/Rari...