It's not unfeasible so much as it's just that there's a lot of it (with 4 main characters of different dialogue? a lot), and no one is actively trying to do it right now. It's a lot of work.
In the end, the plot is fairly shallow. It's unfortunate to not have it because there's plenty of mildly amusing dialogue if it's anything like GoS, but in the end the dialogue is almost exclusively witty banter, so it's not any worse than playing one of the official Touhou shoot'em'ups with translated menus/UI but JP dialogue. The Three Evil Pillars of Evil or whatnot want to turn Gensokyo into more Makai, they're draining all the residents and causing them to turn into Shikigami, and you go and stop them; that's... more or less the whole gist of it. More straightforward than GoS.
On the upside, pretty much -everything- except the dialogue is translated, IIRC. And there's not any cases where you need to know what they're saying in order to tell what you do to progress, since it's pretty much just "keep going forward and you'll beat the game". Compare to their next game Nightmare of Rebellion, which has... enough translated to play it more or less without issue (all skills/items, a lot of the menus), but still scattered JP throughout menus/UI and many images.
