I don’t think it makes technical sense to have one FarmBot move from one bed to another. It makes much more sense to just extend the track and keep the device attached to that one set. As Laird mentioned, the main limiting factor is the number of hours in a day (assuming you solve any hardware difficulties). My FarmBot currently only operates for about 30-60 minutes a day to do watering in the morning and evening, and sometimes mid-day if its really hot out.
But, if you had your FarmBot monitoring the soil often, or detecting and removing weeds, or taking photos, or whatever else, then you could probably have it be doing stuff for 2 hours a day. In which case you should be able to scale up to 12x the size without an issue if you want to fully use the 24 hours available in a day.
But is that really the best? What if its most optimal to water within a certain time period, and then to measure soil moisture within an hour? Then you have to make sure FarmBot can tend to all the plants within a 2 or 3 hour period maybe. And then its idle the rest of the day. It all depends on what you want to do with it.