RE: XPS9560 Bios 1.2.4 bricking systems
I would not be willing to risk downgrading to see if it happens again, 1st reason is the people on premium phone support still argue that you cannot downgrade the bios and 2nd it has taken this long for you to reply.
3rd if it did cause a non recoverable brick I would have to wait weeks for a brand new laptop or run the gauntlet with the pile of 2nd hand untested parts you supply the untrained "engineers" who come to cause cause further damage to our laptops. Let's not go down the so called refurbished line or I will post pics of what one engineer came out with once.
Anyone who does go ahead should have Dell confirm they will replace with a new laptop if it goes wrong.