Hi there,
Just came across Lumen and it seems like a really great tool, thank you for developing it! I see that while development seems active, there has not been an official release since April 2021. Are there plans of releasing any of the candidates from the 0.5.0 line? Is there some set of requirements that need to be met to get a new release?
Yep indeed Lumen is a great tool! With Panel you can build any app you want, Lumen is a sort of Panel extension that is a more opinionated framework for building data apps.
The recent HoloViz projects were originally funded by consulting contracts, you can find some info on that on this page: About Us — HoloViz 0.15.0 documentation. Lumen falls into this category too, and is interestingly already heavy used in production by a couple of large companies. You can sort of guess that by the high number of dev releases it has 
I think the goal would have been to release it properly a while ago! Except that there’s so much work to do on the HoloViz project that this has not yet happened. In particular its current documentation isn’t great, it needs improvements for a proper release to happen. 0.5.0 is in the pipeline though and has become pretty high priority.
The HoloViz is looking for contributors 
We would 
to work with you no matter whether you want to contribute to issue management, PRs, documentation, blog posts, community support or social media communication.
To get started with the code or docs check out the Developer Guide.
Reach out on Gitter to discuss with the developers, join the weekly triaging or join the bi-weekly HoloViz call.