I have several clients who have used their YouTube account to upload all their digitized home videos as unlisted videos. Some have done it themselves and in other cases I’ve done it for them. That’s great for viewing and sharing, but they should still keep a local copy and a backup.
I don’t know of any specific limitations with iCloud and video, it’s just that I’m not that familiar with it and don’t know how well it would work with long-form video. For examples, if a converted film reel is 20 minutes long, does that work well? I just finished a video conversion project of 75+ tapes, many of them a full two hours of playtime. I don’t know how that would hold up on iCloud if there’s a lot of long/big videos.