The rumors have been pretty consistent that such an 8x4 chip will exist, and all the most recent reports suggest
it could be called the A14T (at least internally). As far as I can tell though, every recent leak regarding the Apple Silicon chips has focused on three versions: A14, A14X, A14T, and every single report has pegged the A14T as being an iMac chip. This has been repeated enough that I'm starting to wonder if we won't see the 8x4 chip at all this fall, with it making its first appearance in the redesigned 24" iMac (and probably the 16" Macbook Pro) in the Spring / Summer. If that's the case, that would mean that the first 13" Macbook Pro with Apple Silicon will just be using some version of the A14X.
It seems strange (and unlikely?) to me to release an Air and a Pro with the exact same chip in it, but I feel like the rumors may lean that way at the moment. Presumably the A14X variant in the pro might have more GPU cores or something (maybe they call it the A14Z), but still the same CPU configuration. If the A14X performs anything like extrapolation suggests it might, a Macbook Pro with that chip would still significantly outperform a hypothetical Tiger Lake MBP variant, so it's certainly not beyond the pale that Apple might see that as sufficient, especially if paired with big gains in GPU and battery life.