If you are STILL on the Tbolt, then you likely aren't a power user. HTC one is NOT coming to VZW. VZW got the DNA instead, and it pales in comparison. Until HTC can prove to VZW that it can sell like the S3, HTC has no leverage in dealing with Verizon. After the S2, samsung forced VZW's hand by not catering to them, and offering the SAME device on separate carriers. Once the S3 and it's projected popularity VZW had to give in and take it the way Samsung was giving it. They got the locked bootloader they wanted, but nothing else. So HTC is taking a play from Sammy's book. It only hurts the manufacturer to make separate models for each carrier, and until VZW is pressured by sales numbers, or force to by the manufacturers, they will continue to try to dictate what they get.
So, after all that, If you are going to lose the unlimited, then pay the cheapest price and get the S3. Still a darn good phone and will last 2 more years. If you take the suggestion above.....upgrade one line to the S4 and lose unlimited, and when it arrives and is activated, transfer the upgrade from the unlimited line to the other line and order another S4. You will keep unlimited on one line, but lose it on the other. This way you still get the subsidized price for both without losing both unlimited plans.