There is no such thing as I 0 so it becomes a 1
Legitimately curious why you say this, as the rulebook allows for zero-level characteristics.
I am not sure what happens when you try to force an Initiative below 1 (personally inclined to just say that 1 is the bottom) but regardless I do not see "unable to attack" as a valid interpretation.
I have no dog in this fight, was just passing along an observation as I can see either side of it. If a model's strength, toughness, or wounds is reduced to zero it dies. If its WS or attacks are reduced to zero it cannot strike... whether right or not, I can see why someone would assume initiative works similarly to WS or A of 0, especially when the combat rules explicitly say there are 10 initiative steps, ending at 1.
HOWEVER... GW also explicitly included rules for what to do with nearly all zero-level characteristics. If they wanted I0 to have no attacks, why not include it with the part about WS or A like they did when they grouped S, T and W together. You could also argue the 10->1 initiative was an oversight, and I0 just goes after I1 (meaning after power fists, axes, and models charging through terrain without grenades).
All-in-all I can see both sides and the solution does not appear cut-and-dry, to me at least.