I think in order to release the first working version with minimal functionality, you need to do the following:

• Seed particles from arbitrary geometry Seed from arbitrary geometry #5
• Add simple colliders Sphere colliders #17
• Ability to specify domain boundaries using cube object not necessary
• Ability to specify a range of frames for simulation
• Add the ability to visualize and render particles
• Add sand material model
• Add simple documentation (nodes descriptions, workflow, installation, using)
• Make release script Create make release utils #38

After the implementation of these features, it will be possible to advertise the simulator to get more feedback, tips, help with development.