It's being used to host old RPG Maker games like Yume Nikki on NicoNico Douga, which is a significant Japanese content hoster, so I would say it's come pretty far along.
It's worth noting that it's user content rather than direct usage by NicoNico/KADOKAWA, so the lineage is less direct.
However, given that RPG Maker 2k/2k3 games often have compatibility issues running on modern Windows, it would make a certain sense if KADOKAWA used EasyRPG as a way of extending compatibility. Then too, I'm not really aware of their relationship to the games produced with their tools (even ones that could be considered historically significant, such as Yume Nikki), so I don't know how likely this outcome would be overall.
https://game.nicovideo.jp/atsumaru/games/gm20856
Anecdotally, I've used it to play a few RPG Maker 2003 titles to completion on a Raspberry Pi.