I wouldn't call it ret-conning. In Episode IV, Obi-Wan wasn't forthcoming with Luke in that aspect. He just said that he knew his father, etc.
It's not like Alec Guinness said "Well, I handed you as a baby to your Uncle Owen and spent the last 20 years secretly watching over you." That's kind of what this show is for - exploring that period of time where Obi Wan was in hiding.
I loved the trailer and am really looking forward to this - it was the single show I looked forward to the most when Disney+ was announced years ago. Seeing Ewan again is going to be awesome.