my personal view is capaldi is the new batch of 12 and the 13th Doctor, metacrisis doesn't count cause he's human, and to me Capaldi is akin to the Hartnell in age sorta, and will be getting younger as the doctor regenerates to 24. I also remember that the Valeyard is supposed to manifest during Capaldi's time, and can't wait to see that play out!
What I posted above is not my, or anyone else's, personal view, but what was explicitly established in
The Time of the Doctor. The metacrisis double himself doesn't count, no, but the amount of regeneration energy used to create him does.
When Clara points out that he's number eleven, the "Eleventh" Doctor replies; "Are we forgetting Captain Grumpy? Hah? I didn't call myself the Doctor during the Time War, but it was still a regeneration."
Clara: "Okay, so you're number twelve."
The Doctor: "Well, number ten once regenerated and kept the same face. I had vanity issues at the time. Twelve regenerations, Clara. I can't ever do it again. This is where I end up. This face, this version of me."
The Valeyard may or may not manifest during Capaldi's time, depending on whether the production team decide to go there. They paid lip service to him in
The Name of the Doctor, but he's not necessarily a fixed point in time. He was supposedly an "amalgamation of the darker sides of [the Doctor's] nature, somewhere between [his] 12th and
final incarnations." That would suggest that this has already been averted, as we're now on a whole new regeneration cycle - he
would have manifested between Tennant and Smith (the twelfth and final incarnations of the Doctor's original cycle), similar to the Watcher or Cho Je. Don't be disappointed if we never see or hear of the Valeyard again; I think that ship has probably sailed.