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Just going by steam sales and reviews it has probably sold more copies there than in Fanza+DLsite combined. Not counting GOG sales either. If you sort games by popularity on Kagura's site, this games is at the very top.
But the most important factor is, the Chinese market, they are the main contributing factor here. The game has over 8K reviews on steam and only ~500 are in English. Kagura is a Chinese company and also sells a Chinese version on steam, and for what I've heard, the English version sales are a drop in a bucket compared to the Chinese sales. Like I said before most of those reviews were in Chinese. They probably make a small profit with the english translation, but still choose to release it simultaneously with the Chinese version.
In conclusion, it is probably one of, if not their best selling game, so they will very likely give it priority over other games once it gets released.