It's great that you are extending weewx and contributing. I want to
suggest something else you might want to look into, although it's more
complicated.
weewwx excels at
dealing with weather station hardware
converting/regularizing weather data
storing weather data for the long term
making graphs and webpages of weather data
with mqtt extension, publishing data to MQTT
probably other stuff I forgot or don't know about
and while software can be extended in any direction, it sounds like you
are crossing into home automation. I think it makes sense to have a
weather thing and an automation thing and connect them, rather than
making one that does it all. (This is about sharing and reuse, nothing
fundamental).
For home automation, I use Home Assistant (also python), and I have
weeewx post data to MQTT and ingest that into Home Assistant. So I'd
awnt to have a Home Assistant integration for knx, so that you can
manually control it from the UI, write rules, have HA send the weather
dat to it if that's how it works, or perhaps you'd want the logic in
python and not use the builtin logic.
As an example, I have rules that change lights depending on how bright
it is outside. not how bright it should be based on time, but based on
the solar radiation sensor from weewx via MQTT. This sounds a bit like
what you probably want with blinds.
I don't mean to say you shouldn't do what you are doing. It certainly
makes sense and sharing it helps others. (In fact, I didn't know about
KNX and will now look into it!) I'm only writing in case you didn't
know about Home Assistant or hadn't considered it.
It turns out others have already done things you might find useful:
https://www.home-assistant.io/integrations/knx/
Greg