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.