Zedz

I think while it is possible for H4O2+ to form due to the extra lone pair on H3O+, it is highly unlikely. This is mainly down to the fact that H3O+ and H+ are both positively charged ions and would generally repel each other, however I am aware of exceptions to this rule, but this would only strengthen the argument that this reaction is possible. So while it is possible for formation of H4O2+ to occur, it would be very rare, at least to my own knowledge.