To me, the iPad Mini and a 6+(insert any other phablet) have two separate uses.
When I get home from work, I either keep my phone in my pocket or stick it on the charger and pull out the iPad and use it to mess with my fantasy team or send out a few emails while I'm watching ESPN or something like that. I also grab it when I'm traveling and want a larger screen but don't need a laptop. For me, the iPad is more of a coffee table or nightstand device or something you take with you on a trip. A phablet device can fit that role in a pinch but between the aspect ratio and screen size, it just doesn't completely do it for me. To me, the magic and usefulness of the iPad comes with the 4:3 aspect ratio. It's the reason why doing much work (or leisure) on a phone hasn't really appealed to me or why I've never been interested in 16:9 or 16:10 tablets. Manufactures like HTC, Asus, and Samsung are just starting to catch on to 4:3.