Currently the answer is, we don't know.
Neither Dan nor Tom are planning to stand for LARPO at the next AGM (in March 2018).
Obviously at this time someone else can stand and take Memento Mundi off our hands. However, if you are potentially interested in trying to stand for LARPO with a new system, this is probably the time to start thinking about it. We will make time in the schedule for you to run playtest adventures, both to work out the kinks of the system and to get people interested in your setting.
Systems being presented as possibilities will be listed below.