For me, mobile means slip inside my purse and bring it everywhere. For the most part, I already use my 9.7" iPads when I'm out and about in situations that most people would use iPhones (bar taking pictures). In that regard, the Pro 12.9 isn't mobile for me.I'm surprised at the number of people who feel that the 12.9" iPad Pro is not mobile. I use mine all over the place. I am very comfortable reading in bed with it either propped up on my bent legs or just resting on my chest. It is totally mobile and very comfortable to use lying down or sitting in a couch.
Around the house use or bringing it to work everyday though, that's very easy for me. Pretty great during meetings when I can just bring up the PDFs on the iPad of documents I forgot to print out.