Moving plugin to Rhino 8

Can Eto completely replace System.Drawing?
For grasshopper components, the icon still requires System.Drawing, I cannot use Eto.Drawing

You are correct, for Grasshopper you would still use System.Drawing which works on both platforms. I would recommend using Eto for any additional dialogs/forms, however. All of the dialogs in Grasshopper have been re-written using Eto for Mac support.

Hope this helps!