It seems that the feature is still fairly early in the development process, as the site says that internal testing is still in full swing. External testing, by way of a specially selected focus group, is planned for next week.
What's that, you want to hear more about mechanics? Very well. Keeps act as a "starting point" for guilds in the territorial control system. Each keep awards control points (CP) that can be spent on towers and "various things." Keeps also feature an overseer NPC who provides extra protection, sells goods and features, and more. Finally there's the prominence system, which involves earning prominence points (PP) through various methods including PvP and PvE. There's more, of course, but we don't want to deprive you of a chance to visit the Mortal Online website, so off you go.