With rare exception, I wouldn't buy a lens with the intention of using a tc on it; especially for things like sports that require good af (which would be hampered by the addition of a tc) or wildlife which usually requires good resolving power for feather/fur detail. In my experience, a tc rarely performs well unless it has lots of light to work with.
Fwiw, I own the 70-200 f/2.8 IS, a 1.4xTC and I also own the 300 f/4 IS & 100-300 f/4. Of these 3 lenses, i would say that the 300 f/4 IS is the most versatile. It does pseudo macro, it goes long for wildlife & sports, and with its sharp wide open performance and IS it's a great stage/concert lens as well. With the tc it's 420/f5.6 with IS. And yes, I'd rather add a tc to a prime lens than a zoom.
If your interested in a great sports lens, then the 100-300 f/4 by sigma is a killer. I like the IQ of the 300 f/4 IS a lot, but I looove the IQ of the 100-300. Color, contrast and great control of CA(PF in particular) are the reasons why. Oh, and it's nearly as sharp as the 300 f/4 IS - so close that it's a non issue - and all this in a zoom with blazing fast AF.
Personally, I would rather have one of the latter two lenses for your stated uses. YMMV