Anderson was on track to the bigs through his second season in 2008, but after 2009 it was a freefall. He probably shouldn't have even appeared for the Sox in 2010. If 2009 continued to show improvement, he could have debuted then (it took an extra year because of his decreased production).
That would be equivalent to 2021 for a Casas timeline, which makes sense to me. I bet he starts 2021 in AA and he could get promoted quickly if he hits like Beni or Devers did in AA.