On their Facebook page they've posted a couple of statements in the last 24 hours:
A lot of people concerned about this event and a lot of negativity surrounding the human chain from the bottom to the top of the Ben. I have listened to what you are saying and have decided to cancel the event. We will now put all our efforts into another project which is 100 times bigger that the human chain! Saor Alba Gu Brath!!
A further pinned post says:
Sorry to everybody who had signed up for this but I can assure you that this is being cancelled to concentrate on something the full YES movement can get involved with! Several of us have been working on a project which we hope will be ready in a month from now.
Nevis Landscape Partnership had asked organisers to contact them to discuss operational arrangements. They were concerned about the environmental and logistical issues of having 9,000 on Ben Nevis at the same time.