Marsh actually did a video covering it and the Gamegear version which contains said ending. It was the Great Will(Universal Will). A bunch of other gods and stuff you fight on the way there, like Kether, Da’at, Loki, etc.
I haven't watched Marsh's video yet oh my god it's over two hours long and probably won't tonight. But I do know of this "Universal Will" through the wiki:
It's うちゅういしき, uchuuishiki. The uchuu is easily 宇宙, universe/cosmos. But ishiki is 意識, consciousness. Together, 宇宙意識. So calling it the Universal Will seems to be a misleading misnomer of a translation to begin with and it's more like the Universal/Cosmic Consciousness.
Let's compare it to other Great Will names in the series:
無限の宇宙を統括する意識体 (Famicom: むげんのうちゅうをとうかつするいしきたい), “mugen no uchuu o toukatsu tsuru ishikitai”: “Incorporeal entity that controls countless universes.” (Great Will prototype mentioned by YHVH in Megami Tensei II)
宇宙の大いなる意志, “uchuu no ooinaru ishi”: “great will of the Universe” (SMT2)
大いなる意志, “ooinaru ishi”: “Great Will” (Nocturne)
大いなる意思, “ooinaru ishi”: “Great Will” (Nocturne, others)
大いなる理, “ooinaru ri”: “Great Reason” (The Axiom; SMT4A)
Ishiki/意識 only appears in Megami Tensei II's, and only as part of the word ishikitai/意識体--bodyless/formless/incorporeal entity, so it has completely different usage. Simply, Last Bible's is completely different from all the other "Wills" in the series.
My advice is to ALWAYS be skeptical of "connections" that lack overt evidence. Also be skeptical of grand-sounding names and terms that only appear in fan translations on the wiki or elsewhere--it's really not that difficult to verify the translations yourself, with a little Japanese knowledge. A little Japanese knowledge and Jisho are really all I have and needed to prove this so-called "Great Will" variant false. You could do it, too!