Earlier quoted context omitted.
I'm in the same boat, have been watching, love that they have a businessmodel and am waiting for the time when they are covering my needs (face recognition, object / scene detection...). I'd even pay a 2$/month "lurker" subscription which has like 100mb of storage so I can check the features from time to time and support the team.
So this is a project specifically marketed as E2E encrypted, and you are "waiting for the time when they are covering my needs (face recognition, object / scene detection...)" You will be waiting a long long time for that. The only way they can do that is client side, and if they go there we are back to the last few weeks discussion of Apple's new client side image scanning shit. You do not want this service, it seem…
What iCloud Photos is doing for their client-side scanning is: (1) Not to your benefit. There is no positive outcome for you from your photos being scanned. (2) Mandatory if you want to use iCloud Photos.
In contrast, I presume this would be- (1) Only to your benefit, because all of this derived metadata around scenes and faces would also be encrypted end-to-end as part of the photo library. (2) Entirely optional.