Horwath
Legend
Why are you starting with 3e? There was 25 years of D&D prior to that, so if you're going to look at edition trends, you really need to look at every edition. And when you do that, there's nothing that would reliably predict a new edition in the next year or two.
from 1999. D&D is under Hasbro and they didn't buy WotC just for flavor, but for profit.
Also from former editions the time scale between edition is reducing.
AD&D(1st ed) 1977
AD&D(2nd ed) 1989 - 12y
AD&D(2nd ed revised or 2.5e) 1995 - 6y
3.0E 2000 - 5y
trend is to reduce the time between editions.