A long time passed. Still might be relevant to someone.
We have developed a HubSpot app that might be the solution to the problem. It allows sending push notifications for subscribers in the browser. Currently, it is in the early stages. We are figuring out whether there are people interested in a such service.
Please, try it out and let us know what you think. I’m here to answer any questions you may have. Cheers!
web-push-hs.kohorta.co