Would the powers that control Zelensky even want that…? I doubt it.
Nope, nobody in actual positions of power in the west wants Ukraine to bomb the victory day parade unless they're going full brigadier general ripper and want to stop the russians sapping our bodily fluids.
Its a question of whether we actually have the level of control over the UA forces that we refuse to acknowledge we have. I mean, we still maintain our proxy war deniability and insist we're just facilitating Ukraine carrying out attacks independently, while the unproven assumption is that US special forces are on the ground in Ukraine operating the long range weapons so Ukrainians don't have direct control over them. And if that's the case, we don't have anything to worry about. But if we're giving any level of control over to UA forces, which is what we
claim to be doing, then all it takes is one Nazi going rogue and bombing Moscow during the parade
and so far there have been daily long range drone attacks on Moscow with the parade just three days away, and Zelensky is overtly threatening foreign heads of state who attend it
So even if the odds are still remote, they're looking much higher. A drone bombing either the civilians watching the parade or worse, attending heads of state, or worst of all xi jinping himself, would create such an immediate chaos we can't really predict what would happen but we know it wouldn't be good. Very likely all the countries present would declare formal war on Ukraine, at which point the NATO powers have to decide whether they fight world war 3 or let an RU/CN/etc coalition crush Kyiv
At least Modi got an excuse to withdraw from the parade without losing face, saying he's staying home because of the concerns over simmering war with Pakistan.