Under my opinion Lancia should return, 15 years later of its retirement, stills being the manufacturer with more championships, but until they don't develop a New Delta... It's hardly impossible.
So, more reallistic, considering the future WRC based on S2000 cars, hope for a Toyota return, specially considering his rule in F1, Fiat and Peugeot (very difficult if Citroën stills being in WRC).