Or even a service that had some sort of ontological tagging of channels and videos, that also reliably notified you when new videos are released on your subscribed channels.
Would this be vulnerable to a legal attack from Google?
That would be amazing. Why support only Youtube though? It could be useful for many other sources/kinds of content!
> Would this be vulnerable to a legal attack from Google?
Not really, no. Rehosting the video could be fragile legally, depending on the actual use-case (eg. education/accessibility exceptions to copyright). But a free-software gathering links to existing 3rd party content is just a standard web page, nothing challenging legally. RSS feed readers are not illegal. [0]
[0] The notable exception being if you're setting up a centralized for-profit service out of it like Google News is doing. In this specific case they're making profit from content created by 3rd parties, which is definitely a copyright infringement.
Would this be vulnerable to a legal attack from Google?