I don't see trenches as applicable for general battles but I would love to see them as part of the preparations for a siege. Where as MTW2 gives you the option to build towers, ladders and rams I'd like ETW to ask you to build ladders, earthworks and trenches. When you come to battle these should give cover to your cannons and provide staging areas for your assault parties.

For the defenders I'd like to see defense upgrades available such as blockhouses, redans, bastions,counter scarps, redoubts and star forts. With ETW locating more features outside of walled settlements smaller fortifications such as blockhouses and redoubts will hopefully be available to defend them.