Maybe i'm using different youtube content to you, but i haven't run into an inability to play anything on youtube on my ipad for 9 months plus now.
Videos blocked from viewing on Android are also blocked from search in the YouTube app for Android, and I think the YouTube app for iPad works the same way. But if you search for videos through Google Search, or someone shares a link to a video with you, you may end up on a "not available on mobile" screen. Does this play?
As far as a replacement for facebook goes.... uh... facebook? They have a number of mobile apps.
According to Facebook's own help pages, Facebook still doesn't let mobile users create a nickname or create a Page, whether through the mobile web or the mobile app.
there are plenty of proper tablet games for both Android and iOS that are promoted via facebook.
True, but "plenty" doesn't help when the specific game that your friends are recommending to you is unavailable. As for bugging the developer of this specific game to port it to iOS, I thought it cost substantially more for tools to develop a game for iOS than for SWF. For one thing, you will likely have to replace your current computer with a Mac.