Will Verizon continue Unltd Data?

I've been an AT&T customer for sometime and have a 4 line family plan with each line having grandfathered unlimited LTE data.

I've also had a single Verizon unlimited data line for a while. I'm in the Philly market and find that AT&T and Verizon are pretty much equal in coverage and reliability. Both carriers are competitive in pricing.

There are some things that I don't like about AT&T which are throttling LTE at 5GB and no offering on unlimited mobile hotspot. With my Verizon line I find myself tethering on our iPads often especially on the weekends when we attend our kids sporting events. Our kids wrestle so there is a ton of downtime between matches. At work I also find myself tethering on my iPad when I have downtime which is often and often I can't access WiFi.

3 out of the 4 lines in the plan uses 15GB'ish a month and the other line uses about 3GB with a total average 18GB'ish/month.

As I said we are grandfathered with AT&T and my 1 Verizon line is grandfathered. I have an opportunity to take over someone's Verizon 3 line unlimited data plan. And have someone who would take over my AT&T family plan. Yes I know AT&T doesn't work the same as Verizon in AOL but this person can get it done. I also read that other people can get it done.

I'm not really too concerned about not being able to upgrade at subsidized pricing to keep unlimited data. I have an AT&T iPhone 5 that someone wants me to swap for his VZW iPhone 5. The other 3 lines in our family plan really like the Nexus so that's not a problem picking up 3 Nexus's in good condition for $250 each.

My concern with completely making the switch to Verizon is if VZW will continue to grandfather unlimited data and mobile hotspot. I know that you either have to buy a device at full retail or bring in your own used device.

Any comments or suggestions?