Okay I think there is a way to transcend omnipotence and achieve omnivastance but this is still a theory so here we go , so we know that we can't use any other power to gain omnivastance but we also know that omnipotent beings have creators (which are us or something else) but if a being found a way to transcend everything they would have absolute omnipotence.
Once they achieve absolute omnipotence above every fictional plane including the gods that exist within them they would have transfictional physiology but they don't have have omnivastance but absolute omnipotence and the final thing they need to due is 1. To transcend their creator (which again is us ) they could either fuse us with themselves or just kill us this 2. Once they done that they would have to fuse every transfictional being within himself or consume a "OMNI-CREATOR " once they have consumed either all transfictional beings or a omni-creator they would ultimately become a omnifictional being a.k.a achieved omnivastance.
I know some won't think that this is possible because of many things like The omnipotence paradox and the nature of omnipotence but this can be a possible way to go beyond omnipotence and have power that dwells in the unknown, so tell me if this makes sense or what can I improve upon it .