Why I'm concerned about Tahm Kench
Let's ignore his present balance and assume they'll eventually give him the needed changes to make him approximately balanced. My main concern is this: I believe a little thought makes it clear that his ult is incredibly powerful. It's kind of like double-Twisted Fate ult. The ability to move two people such a large distance around the map can set up ganks and dives very efficiently, and Tahm's E makes him very good at tanking turret shots. The problem is, it's very difficult to get people on the same page for those coordinated plays in solo queue. (See the linked video for some examples of how hard it is to get people on board even in high-level play; admittedly, it's early-going right now so people will probably improve some over time.) All this makes me think that if they balance him for teams, he'll be significantly underpowered in solo, while if they balance him for solo, he'll be overpowered in teams. Since I play pretty much exclusively solo, I have no intention of ever learning to play Tahm Kench.
And that's not even to mention his troll potential (on W and R).