No, they won't force you to update to 8, because 7 is still supported, but if you were on 7 and purchased a standalone license with 7, then you would find yourself in a bit if a bind because not only did they drop support for standalone vaults, but they also shut down the servers provisioning standalone licenses, so you couldn't even purchase one now if you wanted.
In short, what they are doing is forcing everyone to the subscription model. If I wanted to go up to 1Password 7 from 1Password 6 because they are supposed to have a AS/M1 version of it, I couldn't because I couldn't get a standalone license for it. I'd have to purchase a subscription to use 1Password 7 or newer, as it would leave my standalone vault in read-only mode until I purchased that subscription. Reverting back to 1Password 6 wouldn't fix it either, as the vault would still be stuck in read-only mode. The only way I could get back to a functioning standalone vault would be a full TM restore from a backup I took before I tried to update to 1Password 7.
That said, if you are still on 7, the difference with you going up to 1Password 8 is that they would require you to store your vault on their servers, and not a cloud service of your choice (read: Dropbox, iCloud, etc.).
BL.