I think tcpip is a poor choice for a tag name. I would even say the term TCPIP should in general be avoided.
Sometimes the term TCPIP is used by people talking about the entire protocol suite including those things unrelated to TCP. In those cases "The IP protocol suite" or just "IP" for short would be better terms to use.
Sometimes the term TCPIP is used by people who don't really understand the boundaries between the different protocols. And I have seen people use it, when they actually should have said UDP.
Anybody specifically talking about TCP and knowing the distinction between the various protocols in the protocol suite would be more likely to simply say TCP than saying TCPIP.
So making tcpip a synonym for tcp is probably going to have a lot of questions tagged as tcp which shouldn't have been so. I think it would be better to make it a synonym for IP protocol suite or something to that effect.