If I look at the sub-forum of Plasma Mobile, it seems to me an almost non existing community. What do you think? Does it makes sense, to invest time in this project? If there another place, where developers talk about Plamsa Mobile? I like the concept of Plasma Mobile very much, the convergnece UX and the freedom of customization - at least concetually.

I've seen few posts around here for Plasma Mobile - different people trying to get it working on certain devices. I suspect that for now at least it is mostly hobbyists and enthusiasts who want to try it out.
However, that could well change with Purism's Librem 5 phone which is expected to be able to run Plasma Mobile (as one of its two primary UI systems, the other being Gnome Shell or a derivative thereof).
That is, that is really the only major effort to get Plasma onto a mobile device currently underway that I know of.

That said, I would love to see this come to fruition. At the very least I've considered trying to put Plasma Mobile on my LG G4, but never seriously enough to investigate if that is possible and/or what all I'd need to do to do it.

Thanks for your response. It seems, that Purism might support Plasma Mobile as an after market option, but They are focussed on Gnome Mobile. I will try to get in contact with Purism to discuss synergies with our investment in an alternative ans free pre-installed OS for consumer devices.

Plasma Mobile seems to match best with our plans for an innovative UX. At least concetually it supports a convergence use case and completely customized UI. But to bring this system to a stable stage for a commercial product it requires many man years, to much for one company. Only large companies like Google can efford to create an operation system Fuchsia from the scratch for the next generation Android replacement.

My company thinks about hosting an event for companies, entrepreneurs and developers with a boot camp character to find synergies for an alternative OS. An alternative needs this synergies to enable an alternative, that is not an after marked system. What do you think about this kind of event?

There are some more alternatives out there: UBPorts for example, that is not supported by Canonical any more and will drop the concept of scopes.

My company is looking for an OS layer, that enables a flexible and easy hardware support, core system services like network, camera, phone support and also messaging, contacts, events etc. The core layer should be flexible enough to enable different product concepts from notebooks, phones, tables to wearables. They should be able to run responsive apps. So the development is attractive enough for developers. This is the concept of Plasma Mobile, right?

I'm open for any recommendation. Maybe we should think about a lower level of synergy like Halium.