I can't see IAG being allowed to purchase easyJet without major slot divestments in London (LGW for sure, but possibly LHR too), Barcelona (Vueling is the largest airline, by far there, Iberia, BA, Aer Lingus, Level and Air Europa are decent sizes there too), Paris CDG (easyJet & Vueling), AMS (easyJet and Vueling), MAD (Iberia and easyJet also Vueling, BA, EI) at least. There may be other city pairs where easyJet and Vueling compete, Im not sure.
Overall Wizz and easyJet seem more compatible, or IAG and Wizz. I don't see easyJet being attractive to AF-KL or LG for the same reasons of major overlap in the home markets and resultant divestment of slots. Things might change once the EU is done with the Iberia/Air Europa merger, but a lot remains to be seen.