Andrew - this is a good challenge and you have done well so far so thank you for bringing this to the community with a workbook asking for assistance. I have been playing with this a bit and have not made headway so I am asking a few of our Ambassadors to see if they might have an idea about how to tackle. This would be a good post to hold for future multi level dimension ranking/sorting to help others.
I changed your Dimension 2 Collapsed calculated field to
if [Parameter 2] = 'None' then NULL
elseif [Dimension 1 Collapsed] = 'others' then 'others'
elseif [d2 rank] > [Top Parameter 2] then "others"
else max([Dimension 2])
that seems to have solved your labelling/display issue if I've understood you correctly....
If I'm understanding what you are looking for, edit the table calculation Dimension 2 Collapsed. Set the partition of d1 rank to compute over Dimension 1 and Dimension 2. It's currently set to table across.
Attached workbook version 2018.1.