I do think Rowlet is evolving first, actually. Moreso because Ash's birds tend to evolve before his starters, but it still plays into this rivalry.Just a thought I had but if they really wanted to have a rivalry between Litten and Rowlet maybe they could have Rowlet be the first one to evolve or even be the first one to fully evolve and on top of that what if all of Ash's other pokemon wind up fully evolving as well while Litten stay a Litten for a longer period as this could frustrate Litten as it would feel like it's falling behind being the only one not to have evolved at least once or master a Z-move and this eventually leads up to Litten finally fully evolving and mastering a Z-move.
I think earlier, I predicted Dartrix sometime between Trials 2 and 4 (but closer to 4) and Decidueye towards the end of Ula'Ula Island. Maybe even before the Ghost Trial at the earliest for a Ghost vs. Ghost fight. And I based those predictions around when Ash's birds normally evolve.
I don't know about Torracat, but I have my own prediction for Incineroar. But it's really just a guess with no bearing on anything. Something sentimental, you can say.