Notice, that neither tried to combine the two into a single place. They didn’t try to make their community about a broader, more encompassing topic, such as collectibles or music. Both Peter and Jon understand each community has a unique identity.
A lot of organizations don’t get this. They build a single community for multiple products, multiple interests or multiple audiences. A clear, strong (or as Seth would say, weird) community identity is the key element of keeping a highly engaged audience. When you dilute the community identity, you directly reduce the amount of activity.
It’s far better to have many, smaller (and stronger) online communities for each specific interest than one big, weak, diluted mess.
Don’t mix your community’s brands in an attempt to bring them together. It’s more convenient for you, but can kill your community.
Do the opposite. Find ways to push them further apart. Find ways to provide each their own place to really geek out. Identify opportunities or create very tight and highly active communities on a platform just for them.
Sure, it’s more work – but it’s far more successful.