The Seahawks signing of a 6-8 former basketball player has highlighted for me what they are probably looking for in a wide receiver as well. You might point to Tate and Butler as examples of shorter receivers they've drafted, and Baldwin as another, but they cut Butler in favor of taller receivers, and spent much of last off season and into the regular season trying to challenge Tate with larger receivers.
I think this trend will continue even more so with Russell Wilson at QB. Not only because of his height, but because he excels at throwing the jump ball and leading the throw where only the receiver can catch it. Doing that requires height, length and leaping ability from the WR. I think one of the traits the team is looking for is catch area.
I figured catch area as function of wingspan and rise. Wingspan equals arms plus shoulder width (roughly 24 inches) . . . Rise equal height minus head (roughly 12 inches) plus arm length plus vertical. Used an online ellipse calculator to figure the to figure the catch area.
Compa these two highly rated receivers . . . Anonymity makes it fun, even though by my bias you can easily figure out who is who . . .
WR1 - 5'8", 30 inch arms, 32 inch vertical . . . Wingspan = 84 inches, Rise = 118 inches
Catch area = 7,784 square inches . . . Seems pretty big
WR2 - 6'4", 33 inch arms, 40 inch vertical . . . Wingspan = 90 inches, Rise = 137 inches
Catch area = 9,684 square inches . . . Almost 25% more area to throw to!
In a game of inches, that can make a huge difference.