EASA will be an ICAO recognized entity when it has a membership - which it doesn't. The Chicago convention which forms the basis of ICAO treaty recognizes sovereign states independently.
EASA can never have membership of ICAO but then again neither can the CAA or FAA. Membership of ICAO goes to the contracting state and not to any body that they have established to meet their obligations under the Convention.
The is no sperate ICAO Treaty. The Chicago Convention is it. It does indeed recognizes sovereign states independently. However, contracting states are free to cooperate on safety oversight and there is nothing in the Convention to prevent a number of states from apointing the same body to undertake tasks on thier behalf. Indeed regional cooperation is encouraged by ICAO.
The status of EASA the body appointed by the UK to fulfill certain tasks is fully recongised and accepted by ICAO. The is made clear in the Report of the ICAO audit of the UK. The fact that a large number of other contracting states have also appointed EASA to undertake those tasks is irrelevant to ICAO.