It's not impossible tho, GKMC crushed expectations on release, nobody saw that album doing over 150k in the first week let alone going platinum, not in the era of J.COle, Kanye West, Jay-Z, Wale, Kid Cudi, Drake, Lil Wayne, Eminem.
Kendrick has 2 grammies to his name, a double platinum debut, a huuuge cult following/fan base, one of the hottest teams in rap and we still don't know much about the album so that element of surprise is in the air. The biggest difference tho is he gave fans a release date whereas Beyonce and Drake came without warning and did those numbers (plus Drake dropped a mixtape not even an album). It's highly likely Kendrick Lamar will do over 700k in the first week. Shit J.Cole did 650k in his first week and he didn't have all those factors that Kendrick has going for him so a million in a week is not far fetched......