Tactical turn length:
I really like the ideas where combat goes for x turns, and then suspended until the next game turn. This gives a lot of room for strategic reinforcement. I'm excited by the idea of two players rushing reinforcements to a battle, and having a small pointless skirmish slowly turn into an epic battle that determines the game.
Also, on the tactical level, it gives you scenarios where you just need to hold out for the day until reinforcements arrive. Both sides of that could be fun. It would give you real reasons to play defensively or aggressively.
On a side note, it would be good if other players have full access to start making their next move, as well as watching the battle unfold.
Other mechanisms to speed up tactical play:
1. Streamlined UI -- It would be good if you didn't end up giving the same units the same orders turn after turn. Some memory would be really handy here, so at least the last command was remembered. In my opinion, the more complicated this is the better. I would gladly spend half an hour setting how a unit behaves under different situations, as opposed to selecting "Attack this guy with this weapon/spell" over and over again.
2. Crossing a Morale threshold causes all units to route. At some point, your army breaks and all units head for the hills. This will make things much faster since one of the players no longer has to do anything. It also makes morale more important. Strategically, fear based attacks, and morale boosting spells become really important. Plus, if you route an army with nowhere to retreat, then poof, they are gone.
3. Morale loss over time. Each side suffers morale each turn. This is reduced by how much damage you are dealing. This will give incentive to attack, and should force the fights to be shorter and more brutal.
4. Chess clock: If you are the last person to enter your move, the clock ticks against you. The slower player gets penalized with morale or luck modifiers.