When viewing a Project's Plan page, you should be able to sort by the table columns just like you can in other tables.
Currently, you aren't supposed to be able to sort by any column on the Plan page (see KB Article CS37283 and SPR# 2101551) so the Plan should always be sorted by ID. However, there are situations where it could be helpful to sort by other columns. As long as you are then able to re-sort by the ID column, you should be able to do this.
Also, even though you are not currently supposed to be able to sort on the Plan page, you are still able to sort by a Soft Attribute column. And once you do this, you aren't able to sort by the ID column to get back to the default sorting because sorting has been disabled for all columns...except the one I just sorted by.
For example, here I have sorted by the soft attribute 'Gate' which causes my ID column to be out of order:
And then if I try to sort by the ID column, I am not able to:
Enabling sorting for all columns will provide additional flexibility to the users, and prevent this issue of getting 'stuck' with a plan that has the IDs out of order.