Why wouldn't it be intended? To stop trolls from seeing an ally pick an ADC with a channeled ultimate and responding with Tahm Kench so they can turn their ultimates into wastes and then throw them into the enemy team. Redmercy covered this in his League of Myths episode about Tahm Kench, link to that video here, https://www.youtube.com/watch?v=L7mRcu3O6i0 which was released on July 25. I doubt that Riot doesn't have people patrolling these types of YouTube channels looking for bugs, and would have fount this if it were. Another thing he covers in that video is Kalista can ult her Oathsworn into her and they can both take a Tahm Kench's ultimate and several other interesting interactions. At an ally, Tahm Kench's W counts as a buff instead of a form of CC. I'm unsure if he can do this with any ally with a channeled ultimate, even if they can't move while channeling, but he can use it to give an ulting Skarner some movement speed as well. Some of the "interesting" interactions you said down there are ones that would be logical from a realism standpoint, but overpowered from a balance standpoint. Think about it, Riot's purpose is to balance the game as best as they can. Not to change things from the way they are intended because people are getting caught off-guard. Learn from it and, next time, expect it.