Use of Logo on website or youtube videos

Could you please explain what’s currently allowed (until logo registration succeeds) ?
Use on private or commercial sites ?
Does it depend on foundation membership ?

My layman’s interpretation would be that as long as the logo isn’t protected anyone can use it for any purpose ?

Fairly easy, as long as the registration is not finished, the foundation can not define rules for reuse if the logo and cannot grant permission to use the logo. Everyone using the logo right now does this at own risk.
We hope to have finished the registration process by end of April.
It will be not necessary to join the foundation for logo usage, but to follow the to be defined rules.

What sort of risk would that be ?
I may start using it now and forget about usage then logo gets registered and then rules get defined that make my use a forbidden one then the foundation could sue me.
But that will only apply from the logo registration or rule definition day on. It cannot turn my previous use illegal, can it ?

IANAL, so cannot really comment on the risks.
What I can say is if a current usage will be not inline with the to be defined usage rules, this would become some kind off illegal usage.
So it is definitely better not to use the logo atm.

As far I see “openhab” in text form is already registered as an trademark. This means that such representation is already subject of intellectual property rights and its use can be regulated by owner. Lack of such terms & conditions cause risks on both ends - users and owners.

WRT mark itself - there are several registrations which can be listed using WIPO brand database: WIPO Global Brand Database: openhab (this is shortuct link since wipo embeds some json in search string, you can use direct link and enter openhab in search box).