Ideally a new build of C2 would convert existing Tiled BG objects into sprite objects with the tiled image option enabled, then leave it up to the devs to combine them into a single sprite object with frames if they want, unless that can be done automatically.
If that is not practical, then keep tiled BG's around but inform users in the manual that it is obsolete due to the sprite object's new feature, and eventually remove it from C2.
We definitely do not need a whole new object just for one feature. That means 3 very similar objects that must be individually maintained, and can't be used in families.
A "tiled image" behavior is interesting but I don't see it being used on anything other than sprite objects, and isn't even compatible with, say, 9 patch.