I've had every iPad since the first and they've always* been cellular. When I buy the iPad Pro, it will be cellular, too.
*Well, I tried a wi-fi only iPad Air and promptly took it back for the LTE version. 🙂
Yes, I can tether to my 6s+ (and it does it "mostly" without my input) but it doesn't always work automatically, and then it's hitting my 6s+'s battery, too. Also, I want a GPS chip in my iPad. When I take it on the road, I want precise directions. Also, if for some reason it gets swiped, I want the Find my iPad to be as accurate as possible.
AT&T has given me a $100 bill credit if I agree to 24 months @$10/month in the past...that takes some of the sting out of the data plan. YMMV, IMHO, etc!! 😀