An IEO is an Initial Exchange Offering (if I'm not mistaken).
As long as the IEO provides benefits for the exchange, I make sure that the IEO will continue to exist anytime.
Centralized exchange has the goal of seeking profit, as long as there are benefits from the various programs, I make sure the IEO will continue to exist.
For about other methods but ICO, IDO, IEO I admit I don't know yet because maybe this is my limitation for cryoptocurrency.