Okada is a fantastic wrestler and talent who's transformation since leaving TNA has been magnificent. From Samoa Joe's lackey to NJPW champion. TNA really did miss the boat there.
I don't think it's fair to compare anyone who signs for WWE these days to someone like Yoshi Tatsu, since Tatsu was signed at a time when WWE were operating under a different policy. WWE don't sign people these days unless there's a plan in place for them, much like they don't call people up from NXT unless there's a plan in place for them.
Another point is that Okada would be a much higher profile guy than Tasu or any other Japanese talent that WWE have signed for a long time.
I think he'd be a great asset to WWE if signed.