For example, for me, here are some things I wish to see (or would implement in my design) :

• design around ease of self-hosting. A non technical user must be able to self host easily and at a very low cost.
• Embrace content sorting and filtering algorithms, but on the client side, with optional control by the user.
• Standardize tags on all content. So many of the different ways different platforms classify or organize content can be implemented as tags, which increases interoperability between them.
• Abandon obsession with real-time-first implementations for use cases that don't explicitly need it.
• Transferable user identity (between instances)
• User identity and authentication as separate service from social network instance

Would love to hear yours!