Changes to 40K 6th edition and rumors from upcoming books have gotten my thinking, and I'm really looking forward to more of this edition, because I think we're going to see some really interesting things and some total craziness.
We should certainly expect more fortifications, with their own rules. We should also expect to see units and characters that interact with fortifications in special ways. Perhaps a certain character will allow you to bring an extra specific fortification along included in his own cost? Maybe we'll see characters that allow you to reposition someone else's forts, or redeploy your own after regular deployment? Bonuses to the AV/save, or bonuses to destroy them? Maybe an Eldar Bonesinger will be able to repair Eldar-specific buildings?
Allies have shaken things up significantly already, and with the wide and ever changing possibilities for combinations, will keep things interesting for those who want to keep trying new things. One of the Dark Angels rumors is that a particular character will restrict their allies further (preventing IG allies). If they run with this, we could see similar things for future releases, where different units or characters change the allies chart for you. Some that forbid certain allies, some that open them up, some that change the level, like making those Allies of Convenience into Battle Brothers or vice versa. Imagine a new unit in the Tyranid Codex, Genestealer Patriarch, that opens up IG as allies for the Nids? Imagine the ability to mess with the other side's allies, like a character that sows dissent among the enemy and knocks them down a level, from Battle Brothers to Allies of Convenience, from AoC to Desperate Allies? That would be sure to foul a few plans.
We've already had hints that army and character specific Warlord Traits are coming, which will change things up. But we may also see things like the ability to nullify enemy traits, or force them to re-roll and accept the second result if they get one you really don't want them to have.
I really look forward to having all these different options - and the ability to mess with them - as the edition develops. Bring on the craziness!
Except for mysterious terrain and objectives. But maybe I'll warm up to those too over time.