The most obvious PoD is having Catalan never diverges as much it did IOTL from Occitan continuum, up to form an ansbau language.
Having a lasting
Aragonese-Occitan political continuum could only help, of course.
If in this situation, Mediterranean policy of Aragon knows a slight northern displacement, making OTL Lengadocian coast more important (following a Barcelona/Montpelhèr/Provença line), the influence on
central Occitan article systems (central ITTL, including Catalan at least longer) could make it, making salat system being more used at least along the coastline and having Barcelonese *Occitan an important norm (here at least for article system) that would influe on other relativly easily.
It's a bit of cheating of course, at you won't have exactly Eastern Catalan dialects, but almost all Mediterranean dialect of *Occitan concerned.
I don't think it would eventually take on all the coastal speeches (actually, I think it would probably be limited to most dynamic and urban settings), and eventually the "regular" system could likely prevail, but I couldn't see a best chance for the goal you search.