Interesting, I wasn't sure if they were going to allow freeform castle building in the campaigns. I actually don't like that because it allows players to create keeps that are cheesy to defend, rather than give players keeps that have utilitarian purpose outside of sieges.
It's also interesting that they will have these bloodstones spawn during the unprotected state and you have to choose how many players to use to move the bloodstone away. One thing I'll advise is to make it so that moving the bloodstone is slow and its location is very easy to find. Moving the football in GW2's campaigns was a ton of fun. The football in ESO was also kind of fun but you could move it to fast. The football in ArcheAge you can move way too fast and nobody knows where it is (even the faction that holds it often!!!) so you never really have an epic struggle to get a touchdown.
I feel like the paradigm of the bloodstone spawning during the unprotected state is a bit contrived. With these systems I worry that developers have a plan in their heads of how it should go and fuck with the ruleset until the players do what they want. They throw the word 'emergent' around, but they need to be careful with it. One big question I have is what the rewards for owning a keep are. In previous games owning a keep provides very rigid, artificial benefits. You get points in ESO/GW2, you get taxes in AA, I don't even know what we got in AoC or DAoC, lol.
I hope they create a more natural system that provides the owner of the castle with some force projection benefits over a certain area and economic benefits. Owning a keep/tower would provide some kind of radar features in the local area. Maybe you could have NPC guards that spawn and patrol the resource areas and help defend caravans. On the economic side, if we're doing a full loot system, npc merchants that sell player-made goods could only be protected in these areas, and the owner of the area gets a tax for it.