For once, I find myself in full agreement with you. Turalyon has a lot of the makings of a warhawk & has already done questionable things, not to mention his talk about wanting to take back the other human kingdoms. However, he had years to start that effort & the Alliance does not appear to be currently at war with the Horde. He hasn't visibly tried to force the issue. We also saw that he's willing to learn & adjust his past views from his interaction with Alonsus Faol in Before The Storm. Plus we also have to remember that the Light's control over him seems to have faded with X'era's death. His eyes during the Rejection of the Gift cinematic show this being the case.
With that in mind, why would he suddenly go evil? He'll likely be happy to see troops from the Light with Yrel if they invade, may well even roll out the red carpet welcome to them in Stormwind at first. However, given that he's now had years of Alleria at his side balancing him again as well as Velen as an advisor who himself no longer blindly follows the Light (though he is still a follower), he's likely to be a bit more grounded & willing to fight back if they start to try to enslave or kill everyone. The main concern I see on his end (if anything) would be if Yrel talks him into renewing his vows to the Light via the efforts of another Naaru.
Calia on the other hand...I agree with Nymrohd on her being a much more likely threat. The Light specifically wanted to bring her back & used Anduin in part as a vessel to do so. She is seemingly far more under the Light's control right now than Turalyon was back then. She may seem peaceful now, but so did Yrel at one point.