If I may, it does not only support PI, as it support any decide capable of running Java, so I would "wish" for a Devices sub-forum with added topic prefixes, such as "Raspi", "Arduino" or even "Banana Pi"
For sure the [IoT] convention is very usefull for searching the forum. But in the case of Raspberry Pi I can see a lot of different naming from Raspberry Pi to Raspberry, RasPi, RPi, even RB or RP are sometimes also used.I don't think that adding topic-specific subforums will make the forum more organized. It will for sure require more moderation.
You should add [IoT] prefix to discussions related to IoT.
You can then easily search for relevant threads: https://www.b4x.com/android/forum/pages/results/?query=iot
The search engine will also find all raspberry pi related threads: https://www.b4x.com/android/forum/pages/results/?query=raspberry pi