if the tv follow the hdmi spcs then it like any other tv should work without problems
mind you when you mirror ipads you mirror! what you see ipads are not widescreen
so mirror does not take up the whole screen it was not meant to and if it did it would 1 chop the top and button of the image or streght the image
Have you thought about using an ultra short throw projector instead of the TV?
You can get a projector for close to the same pricing and your screen size could go up to 100"
Also, I have set up an Apple TV in a business conference room on a 60" TV. We integrated that setup through a control panel that allowed us to simulcast to 3 other projectors in the room and vice verse to whatever primary screen we wanted to show. this worked out great.
I see on this forum though that a lot of people are having issues with mirroring... And as the person above me stated that the screen is only going to be as large as the Ipad will allow... Most MacBooks can work larger than the 70"