Boo hoo

Your capacity to focus on irrelevant details such as which nationality formed a slim majority in some unimportant piece of land (it's always the Poles, of course) is truly amazing.
if there was a map showing Czechs in a similar light, you'd do the same.
Also, I'm discussing the map and its faults. You are discussing me.
Nonsense. Poland didn't exist at the time and the Poles inside Austria-Hungary were the ones who were better off. They were for most of the time perfectly content with polonizing the Ukrainians and every other ethnic group unfortunate enough to be under their administrative thumb. I guess this is why interwar Poland was so friendly with Hungary which has historically behaved the same. I think it was a response to their national complexes - they felt inferior to the Germans, so they took it out on other, less powerful nations.
Ukrainians were often used by A-H to counter the demands of Poles. What do you mean by polonisaion of Ukrainians in A-H's Galicia? Any examples?
Poland had a long tradition of good relationships with Hungary, originating from Middle Ages. We also had a common foe in the interwar period - land-grabbing Tchechoslovakia which conquered both hungarian and polish ethnical areas.
When it comes to hungarisation and polonisation - Czechs and Slovakians were doing exactly the same in the interwar period and after ww2. When it comes to Ukrainians, they were even worse to their ethnical minorities.
Galicia would have been divided in two to give Ukrainians their fair share of the power. The old days of ethnic expansionism would have ended.
"fair share" = all the mixed ukrainian-polish areas go to Ukrainians. And some majorly polish ones as well. Ukrainian part would have around 35-40% polish minority, polish part would have no ukrainian minority at all. It's ethnical gerrymandering.
Maybe. The Hungarians might have attempted to secede to secure their right to continue the culturecide of their subjects, but they'd have been soundly defeated given that the western regions (Austria, Bohemia, Slovenia) were much more developed (not to mention supported by other countries seeking stability).
Do you really think Czechs would be so keen on letting go "Sudetenland" to Germans, Cieszyn Silesia to Poland? That division of Bukowina wouldn't start a conflict between Romanians and Ukrainians? Not to mention the case of Banat, disputed by Hungarians, Romanians and Serbs?
Had the plan succeeded, we'd have ended up with a stable, reasonably free Central European power that would have prevented all the OTL crap from happening.
No we wouldn't. ANY division would mean conflict. Any. Also, Germans (Austrians), Poles, Romanians and Serbs lived mostly outside A-H's borders and would, at least in the case of Romanians, Serbs and Poles, want to unite with their brethren from outside. The idea you propose might seem natural for Czechs, Slovaks, and, to some extent, Hungarians, Slovenes and Croations. For the rest of A-H's nations, it is not.