We, Nebulas.io are developing a self-evolving network that will be upgradable without the need for a hard fork. This is one of our primary tech goals!
From our white paper:
Nebulas Force (NF) (§3), which supports upgrading the core protocols & smart contracts directly on
the main chains. This will provide Nebulas the capability to self-evolve and incorporate the newest
technologies into the main chain, once they are ready for real world usage. With Nebulas Force,
developers can build rich applications in fast iterations, and these applications can dynamically
adapt to market changes or community feedback.
Upgrades to the protocol/software will be included on-chain so all nodes will be at the same version at all times. In addition, we hope to incorporate a voting mechanism where people can choose what upgrades should be included.
If you are interested in learning more, I suggest reviewing our white paper at:
https://nebulas.io/docs/NebulasTechnicalWhitepaper.pdf and if you have any questions, please ask.