I hope Oda pulls off the Sabo flashback really well. I know lots of us expected him to be either a revolutionary or Kaido pirate of some sort, but both are kinda hard to write…
Revolutionary angle: Hey, guys! I decided at a very early age to become a revolutionary army member -- I'm no better off than those kids in Africa!
Kaido angle: Hey, guys! Due to my tragic backstory, as well as serious injuries, I've been modified into some cyborg or minkman or potato or something to kill you!
Surprisingly, that old Kaido angle seems more emotionally believable. Under most situations, even in OP logic, it's hard for me to accept that Sabo was just whisked away to the New World for over a decade, did solely clandestine revolutionary army missions that entire time, and never once sent a message to Luffy.*
Oh well. Oda doesn't really let me down, so I'm eager to see how he explains the absence. :)