I still think there are still many good european animals which would make fine additions. An eurasian otter (although not strictly european), a european duck, a white stork, a mediterranean pelican, the western capercaillie, maybe a pheasant or heron, a marmot, a squirrel, a rabbit/hare, a mouflon, a chamois, a mink or marten, a wildcat, the common genet (although it's also african)...
But yeah, I also agree that for now it's not the priority. Frontier should focus on South America and on the few remaining gaps in Asia (one or two deers, an Indian monkey, the blackbuck, maybe the nilgai too, the hamadryas monkey for the middle east, an Asian pheasant would be the minimum) to finally have a complete game - then, if there is still support, come back for the few remaining holes in North America (the ABB, the sea otter, the musk ox), Europe, Africa (we need more african monkeys and birds especially) and Oceania (tree roo, more kangaroos).