Hi @Ichigo85,
cool you already stumbled over our new properties panel project, although it’s far away from being “actively consumed”. 
It’s true that we are currently investigating a new properties panel library. In the past, we had lots of difficulties when creating new features with the existing bpmn-js-properties-panel library (and siblings for dmn, cmmn, …). We recently added a lot of stuff, e.g. for element templates. The way the properties panel was built makes it difficult to deliver more features than the original architecture was built for - a 1:1 connection to its data schema, the BPMN 2.0 XML. Some things were simply not possible (or at least it was very hard to implement it).
In the last quarters, we started to rewrite the properties panel from scratch. We already made a lot of improvements in terms of developer experience (how to provide properties / how to commit updates / how to provide the data for certain groups & properties / …) but also usability (more context what did I select / what properties are already configured / open sections in parallel / …).
We are still in the development face and are currently see how to consume the new properties panel internally. Still a lot of things to learn and improve.
So far there is nothing really that is ready to use. The existing bpmn-js-properties-panel is still the library to choose when working with bpmn-js.
When there is something ready to use, we will properly announce it and also give advice, how to consume it… and what cool is stuff is possible then 
How much will change the code?
We have in mind to make the way how to consume the properties panel alongside bpmn-js- and how to provide extensions - as similar as possible with the existing way. There will be of course things that will need updates in existing extensions - but we will
a) make sure the migration need is as small as possible
b) provide examples how to do it
Stay tuned 