Basically Titans are the rarest of war machines, and were created to destroy anything that moves. And they're huge.. we will prolly not have em.
Also - Titans were used mainly as a last resort if the last line defense was breeched during an invasion, in the era of the RTS DoW and WA only one titan remains operational and that was the Hammer varient which was the ultimate of the titans. 
But, you were close hehe, I love the land raider, an tho delayed I am, it just dosn't look right without its manly door chimes ("spikes")
Well my first idea of adding a Titan would be to have some giant pop from one random side of the screen crushing and blasting a path from one end of the map and then to the other. But that seemes a little too dificult
Another idea is to have a Titan act as a land super weapon where a timer is placed till Titan is deployed. When that Timer reaches to Zero it is an automatic victory.
Atackers need to hold a specific Reenforcment point. If the Defenders overrunn that point and attackers fail to secure a hardpoint then the adaptus mechanicus will not risk one of their most holy and preciesous war machine to be squandered by an inept commander.
Defenders need to protect the Titan as it powers up. The Atackers get a chance to destroy it before it becomes activated then they can remove the titan that way.
Problem with the second idea is what happens when you get Titan vs Titan. Well lets save the Titans for an expansion then till we figure out the gameplay and other technical features.
Good game.
