I can confirm that it is definitely possible to achieve a peaceful Revaire ending with following Katyia's legacy with the Arland princess even pre-1.10--it is very tricky, but I managed to do it while aiming to romance Clarmont. There's a lot of planning to make sure you have 250 persuasion by the time week 1 ends so that you can pick following Katyia's legacy for your ambition. You have to make sure that your weaknesses aren't related to persuasion AND likability (unless you have a ton of bonus stats) because with everything going on you can miss some major stat checks while trying to make up for the loss. You don't have to befriend Gisette or talk to her during day 1, but do make sure that you max out your success during the play. Playing opposite her as Serah during the play with perfect success opens up a special conversation with Gisette and increases your respect with her, which will be handy when you try to negotiate for peace.
Interestingly enough, when I try to aim for Revaire peace with other builds I have a lot more trouble. I have tried several times as a Jiyel scholar (my default) and some other builds, and either I can't befriend Sarya and get her to open up, or when talking to her I can't get the peace option to show up.