Where using the supporter's indication of support (the support vote) as an indication of how many support votes the particular plank has, it is not appropriate, due to ambiguity, to simultaneously attempt to interpret the number of support votes for a particular plank to also be an indication of the relative priority the plank should be given among the many.
Many may agree that a particular plank topic should be included in a platform, but disagree on how its priority should be ranked in relationship to the whole. So, a separate field is needed to track such information.
The priority field would then be a useful alternate sorted screen option as well.