Not "Google+" as it's defunct now, but Youtube in a sidebar...
Lack of features. Would be interesting with additional features.
The only thing it does now, is to open in a sidebar your Youtube page, with video feed as the landing page.

I would need options, which subscriptions I want to show, subscriptions lists (as it's not easy to manage subscriptions in Youtube now!), and more...

Permet juste d'ajouter un mini-onglet sur le coté pour toujours avoir sa playlist en cours et la gérer. Moi j'ai des onglets et ça me suffit.