I, like many others, use the desktop app for "heavy-lifting" tasks (guides, research, word studies, etc.) and prefer to use a tablet for longer reading sessions. I have found myself asking why there is no "Bookshelf" feature (not a reading plan) that would mimic the ease and function of the now-defunct "Send to Kindle" feature. It does not seem like this would be particularly challenging to incorporate.
Here's how it should work:
Let's say I'm studying in the desktop app, and I come across a resource, commentary, monograph, etc. that I want to spend some time reading. I simply click the 3-dot menu button, and there I find an option that says "Send to Bookshelf." Then I grab my tablet, open the mobile app, tap the menu, and under the Library Section, I see the word "Bookshelf." I tap this option and a mobile layout populates with all the library resources that I've added to my bookshelf. I select the title I want to read, and I'm off to the races...
Please consider adding this feature soon.