Thanks for your help. And I'll keep in mind that "that backdoor" it is sort of borderline lawful...
I did not refer to that deadline contribution extension for traditional IRA as "quirk", I referred to "backdoor" as "quirkiness". My point was if that deadline is extended, then the deadline for 8606 should be the next year. Because that's what happens: a person fill his return in January. Opens a brokerage account in February, where they told him/her that they actually can contribute to Traditional IRA not only for the current year, but for the previous one too. He happily (and clueless) does it, but then on his next return he finds out that he was supposed to fill some 8606 form that he had no way to be aware about. So, my issue is not about that "backdoor roll over" at all. I would be in the same shoes if I did not find about that possibility (that seems like every "advisors" online talk about).
