I have been working on a volumetric cloud replacement add-on for X-Plane 11 since last two-three months, and finally managed to get visually appealing results. The add-on is not a weather engine, and it only replaces default X-Plane 11 clouds with volumetric ones, therefore it should be compatible with weather injection add-ons like Active Sky XP, as well as the add-ons which only change default art assets, such as Cloud Art and FSEnhancer. Currently it supports X-Plane 11.30+ and two major operating systems - Windows and Linux. It is an open source freeware, and finally first alpha release is approaching, which is expected to be released in a few weeks. Feel free to check the source code out at https://github.com/FarukEroglu2048/Volumetric-Clouds!
Also, if you want to support the project and my EEG research, please consider donating: https://www.patreon.com/VolumetricClouds
(I am a biology major and get funded by my university for an EEG research project, at least to some degree. However I am still supposed to cover rest of the costs by myself, and due to the COVID-19 pandemic, I am no longer able to do that. I was quite shy for asking for donations, and the pandemic is the only reason I ended up creating a Patreon account and making it public. However, I need to make it clear that the plugin will always be an open-source freeware, and there won't be any patron-only benefits other than early build access.)
Lastly, many thanks to everyone helped me in the development process so far, including Saso Kiselkov (totoritko) from Hot Start, @Captain Kitten and mSparks.