Time to write a script to poll the channel pages and give its own notifications on new videos?
I even had the idea to make a separate service that controls subscriptions for users and send messages to e-mail how to in the past.
I consulted with friends and we decided that this service will be tortured by attacks to steal user logins.

Obviously, it is not profitable for google to send messages - you will watch e-mail and many videos from the subscription will not be watched, because in the e-mail you will find that it is not interesting. Now you must open the update page every time.
This is life: a nice, easy, convenient Youtube was eaten by a monster, became fat and still decides how you are better.
