I/O refers to Invitation Only. My understanding is that is status given to selected customers determined by EK as being particularly high value. Others here have that status and could explain what that means better than me. There are no published eligibility criteria as far as I am aware. I believe that criteria might include being responsible for decisions about a lot of high value travel (e.g. deciding travel policy and spend in a large company) or being felt to having a high degree of influence on potential EK customers. I believe that BA have a similar status known as Premiers.
No chance for me on either airline

I do feel that EK provide good service to F pax before flying - chauffeur drive and the lounges (esp in DXB) are very good and I have always found the telephone support to me as an F pax very good. Compares well with QF,SQ, CX and BA in my (limited) experience.