Foxy has simplicity but it has a cost too. The cost is absolutely insane number of games you need to play to change anything.
15-20 games is way too much for anyone who doesn’t play go 24/7. As a result the ranks adjust very slowly (and therefore less accurate).
If I recall correctly we switched to Glicko precisely because our ranks were slow to adjust and mods had to change them.
And it can be discouraging too. When you have one game deciding whether you go up or stay on the same level and you lose. You realize you’ll have to win like 15 games in a row to even get to this position again. And I assume people try to do this thing where they pick who they play because of that. Because every opponent worth the same. Even if they have 20-0 game record or 0-20.
Plus, let’s not forget. On Foxy you play only against your level (or ±1 without komi) for ranking. As far as I understand, there’s no ranked games between different levels. They can do that because they have very large player base. We don’t.
In conclusion, regarding foxy-like ranking on OGS: “No, God, please, no”. I love foxy but in a very special way.
I really believe rating-based system where you win - you get some points, you lose - you lose some points is a way to go.