Eurofed
Banned
Romania for strategic reasons. Bulgaria is in the Soviet field, just like (southern) Yugoslavia. Romania may feel embittered by having been practically abandoned by the West and sacrificed by the Wester powers. All in all, a Soviet option may appeal to some sectors of the population, thus reproducing the Polish and Yugoslavian situation. But this time Stalin will likely wish to physically connect he countries under his heel...
I see. Well, it is entirely possible that Stalin again tries the Red subversion trick on Romania, but if he does, I do expect the Communist insurrection attempt to fizzle and die rather quickly, nothing like Poland and Yugoslavia. This for several reasons: pre-civil war Poland and Yugoslavia were left in a neutral geopolitical vacuum, which armed their economies and gave a sense of national insecurity. Romania is firmly anchored to the EDEL. I reasoned out that TTL Romania would turn out a fairly loyal and stable member of the Euro bloc just like it did OTL for the Axis, despite the losses it suffered, since the situation is quite similar. Romania has been already attacked by the Soviets, and the Romanians have witnessed how much misery the Polish and Yugoslav civil wars brought to those countries, so Communist infiltration would find little appeal within the Romanian people. Morevoer, they don't have anything like the cultural affinity to Russia that Serbia and Bulgaria had.
I may write an aborted Communist insurrection attempt in Romania, but likely it would be quickly snuffed out by the government and put the European powers even more in a Red Scare mood, but I doubt it would be the main flashpoint. The strategic reasons you quote are good, but proxy subversion would fail for the reasons I quoted, if Stalin want Romania, he likely has to send the Red Army to grab it, and this would immediately cause a general war.
Rather, I was thinking that the main falshpoint might be the Middle East. Turkey eventually joins the EDEL, which makes Stalin feel even more encircled and pushes him to grab Iran, either by direct invasion or by using Azeri separatists as proxies. The EDEL sends troops to support the Shah, there are the first armed skirmishes between Euro and Soviet troops, Stalin thinks war is inevitable and orders Suvorov.