We're reaching a point of diminishing returns for new countries. There are a few untapped countries that could have a significant impact; Finland, Thailand, and Brazil, but aside from that I don't think there's much use in adding focus trees for increasingly minor countries that had little or even no role in WW2.
In terms of minors, I'd much rather see Canada, India, Australia, Hungary, Romania, and Yugoslavia get do-overs than focus trees for Ireland, Austria, Philippines, Argentina, whatever; or beyond that, Italy, Germany, and Japan. Even Germany and Japan despite having received new focus tree years ago, they're pretty darn primitive compared to what we get these days. Controversial thing to say, I know; there are many around here who believe that they should never receive content ever again unless it's free; but I'd rather pay to see countries that actually had a significant role in WW2 receive good focus trees than Austria, a country that is annexed in 1938 and that I will never play except in 'meme' games. Keep in mind that, as of yesterday I believe, TFV and the Canadian, Indian, and Australian focus trees(plus south africa and NZ, I admit to not caring about them) are now half a decade old. Whining about paradox 'double dipping' in giving these very old focus trees a new rework doesn't cut much ice in my view, but that's just, like, my opinion, man.
Canada, India, and Australia have content that is historical, but shallow and unfun. Hungary and Romania don't even have historical content as far as I'm aware of it. I'm not particularly well versed in Romanian and Hungarian history, but I thought it was the case that neither Ion Antonescu nor Horthy were fascists; that they presided over authoritarian dictatorships in which fascists played second fiddle. It would be cool to see a more proper and historical, non-fascist content for Romania and Hungary. Iron Guard Romania should be alt-history and receive its own content, same with Arrow Cross Hungary. The Arrow Cross isn't even in the game right now, but it's to my understanding that when Horthy sought to capitulate to the Soviets, a German sponsored Arrow Cross coup occurred. Could be a neat thing to see ingame, kind of like the Fatherland Front for Bulgaria. The problem with things like the Fatherland Front and King Michael's coup is that they are too deterministic and railroaded; it doesn't really make sense for them to happen unless the Soviets are winning against the Axis.