When real nature of ultimate reality is beyond the physicality of the universe, beyond time & space - Which can't be described by the words then what Arjuna saw actually, because he was describing what he was seeing? Was that Saguna form of Brahman? or something else? Because it can't be transcendental aspect of ultimate reality. Has any acharya shed light on this?
Whether it was Saguna Brahman or not, Vishwaroop form was not of the Krishna. it was of the kAla which was superimposed upon the personality of Krishna because of Krishna's yogic powers which he describes to Arjuna in Uttara Geeta. Arjuna asks following question in BG-
BG 11.31: Tell me who you are, so fierce of form. O God of gods, I bow before you; please bestow your mercy on me. You, who existed before all creation, I wish to know who you are, for I do not comprehend your nature and workings.
To which the Vishwaroop form replies thus-
BG 11.32: The Supreme Lord said: I am mighty Time(kAla), the source of destruction that comes forth to annihilate the worlds. Even without your participation, the warriors arrayed in the opposing army shall cease to exist.
So whatever be it, it was kAla. Now, this answer explains the kAla - what the kAla is.