I have edited the OP to take advantage of your feedback on this king of attack
1-6 comfirmation attacks are always possible under normal conditions although you have to be extremely lucky.
What is the issue I try to make more difficult is the possibility of long chains replacing the current
There's nothing magical about the number 6, as I'm sure you're aware. 7-confirmation reorgs or attacks could happen, they're just less likely than 6 (and more likely than 8 ).
I don't think your idea is bad per-se, I just don't think that the advantages it confers outweigh the new vulnerabilities it introduces, but that's just my opinion.
Thanks for your review.
To sum up the case:
Given a block chain(curve) in order for a new block chain to replace it, one currently has to simply stay below the Difficulty bound and make it long enough.
We propose a more strict requirement (to achieve), that the new curve has most of the points below the given bock chain(curve) and be of equal length in order to replace it.
PS.
a)The maths may be much simpler as sum of -1,0,+1 depending on pointwise comparisons.
b)A form of mathematical "measure" of the quality between the current curve and a possible replacement is what we seek