I've bought (and given away) four iPads with Verizon LTE. Exactly 0 people activated it.
This is old data, but in line with newer data I've seen WRT iPad activation rates: http://tabletquest.com/2011/02/disappointing-apple-ipad-3g-a...
The wife would not like to see the tablet around 100% of the time since, with LTE, it'd be a physical extension more than PC's and the phone are now.
2) It would cost money to add the device to your Mobile account
3) You can just use the mobile hotspot feature on your phone and connect through that. Its easy on my Nokia 928.
Hell, half the time I have my wife's iphone connected to my phone via WIFI because she has AT&T (for work reasons) and they suck most places we go.
For business people your arguments 2 and 3 are actually incorrect: I don't want to use my personal data plan for my work. If the device has its separate LTE, it can just all go to my company and I'm done with the costs.
Not sure it's a worthwile tradeoff for everyone though.