In regards to currently non-priority MP modes, I'd rank them in my personal order of preference as:
1) Non simultaneous play option; that is, have the game hosted by a server and allow players to login, take their turn, then wait for everyone else to come in and take their turn as well. Perhaps have a host setup option of a turn limit as well, if a turn isn't taken within 24 hrs, those players turn button is hit automatically for them.
Combat would almost by necessity have to be autoresolve, but that's fine.
Also, ideally, this very same game should also allow for simultaneous turn play if everyone DOES login together. Perhaps at game creation time, there can be a toggle to allow non simultaneous play or not.
If this option was implemented, it'd negate a lot of my own need for PBeM, although I still wouldn't say No. 
2) LAN play.
3) Hotseat
4) PBeM* -- This is ranked 4th only on the assumption that Non-simultaneous turn taking IS implemented. If that is the more difficult option to implement for reasons I can't see, then the order shifts a little. This moves up to my first position instead.
Quick Edit: In answer to poster above me re: PBeM, I think it'd be difficult to get a real representation of this, but I can tell you that a group of friends and I used to play PBeM AoW, AoW2 and even some Civ4 if we couldn't make it for real online play. We would still definitely take this option if presented, as several of us are across different time zones now.
I've also seen other requests in these forums and in comments made regarding Elemental interviews elsewhere querying PBeM with a chorus then of other askers also making themselves known.
So it certainly wouldn't be a deadweight feature.
That said, I'm just infinitely glad there will be MP at all. I'm sure I still would have liked Elemental anyway, but not for nearly so long. MP greatly increases the longevity of a game for me, so I
that already such efforts are going into it and wouldn't feel any need to complain (too bitterly
) if not a single one of my alternate MP features was on offer. But if they CAN be done, even if it's post release, then Yay and Happytiems! 