Each keep will function as a hardened bastion for their owners. Hard won iron, stone and wood erected to stand as a mark of their standing in the Border Kingdoms, and a reminder to their enemies of the bloody conflict taken to earn and maintain it.
Players will be able to build structures like stables to provide cavalry, forges for constructing siege weapons, sentry towers that provide essential respawn points, as well as farms and other resource buildings. These will in turn provide other useful benefits, like perhaps a vendor that will sell items to those who visit the keeps, or some NPC guards.
The difference with a battlekeep is that guilds will have to remember that there will be others out to destroy their hard work, so the investment in the keep will not come without risk!