Blorp in theory could do this. It would need a bit of tuning to really work well under the circumstances you mentioned. For example, feeds only refresh currently when you open them, but I could have it auto refresh all your subscribed feeds when you connect to the internet.
Draft posts and multi account support is already there if you wanna give that part a try. Writing comments offline wont work yet. They may save if you don't close the app before reconnecting to wifi, but I wouldn't count on that.
I'm the developer behind Blorp btw.