Honestly, having played episodic games, I would be really surprised if Midgar isn't the complete first episode. There is a LOT that happens in that, I don't think it would be too short at all. For an episodic purchase, I'd say that it would be more than enough to satisfy me (I'm assuming we're not paying a full £40 for each episode).

That said, if it is a full game price, then I could understand it going through to, say, Junon or something. I think they will provide us with at least 30 hours of entertainment per episode if it is at full game price, if it's at a more episodic pricing a la most episodic games then I'd say it could be as little as five hours of content per episode depending on the price. Personally I'm really not bothered, because to me this is just a tribute and I'm willing to cough up the cash.