Only the same problem as using any other open source thing that didn't catch on: you have a smaller community to get support from, newer things won't be ported

Only the same problem as using any other open source thing that didn't catch on: you have a smaller community to get support from, newer things won't be ported to your platform quickly or ever, and your chosen platform gets less adoption and becomes less compatible over time. I stopped using Slackware when I got married / got a job / had kids, because debian made all my day to day management tasks easier and I no longer cared about knowing deep details about every single package that lived on my system. I'll still install it and toy with it, but I'm not going to push my kids towards using a sandstorm word processor over google docs etc.