Great topic because I was on the same boat. My 12,9 iPad pro is jailbroken and I dont know if I should sell it or keep my IPP. Jailbreak on my iPad is not something I really care about, its more like a device I use to test tweaks before install it to my phone (because I care my jailbroken phone) otherwise, my iPad pro is basically used for viewing media videos.
I want the new iPad pro for the screen because I think the screen of the 1st gen 12,9 iPad is really dark compared to other iPad.
And for the 2 tablet thing, I have an iPad air 2 also and I use both equally iPad air 2 is used more for productivity purpose like surfing the web etc because the format is easier to hold and its more convivial and I also use it to test new iOS beta's. (currently on iOS 11 on my air 2)
IMO having two tablets is more useful than having 2 phones. I dont see myself constantly switching my sim card between my phones but its a matter of tastes!