Well, after the main cast, and in the interview it seems as if he rules O'Brien out, I think Sela or Pulaski make the most sense.
Though, in terms of folks near & dear to Picard, I am not sure Pulaski, nor Sela qualifies, though Tasha surely did.
Ro certainly would. When she choose to leave that really hurt Picard in TNG. And we never knew her fate.
Then there would be ex-lovers/love interests. Vash. Anij. Nella Daren. Kamala. Older lovers he already met again (Jenice Manheim, Marta Banatides, Phillipa Louvois) don't make as much sense.