I wonder how one of the new adventures would run if you allowed 3.x, 4 and 5th edition PCs. There would be quite a lot of averaging to find a certain mooks current life, but it might work w/ a few houserules.
To be clear of what i mean, when 4th fighter attacks mook xyz, use the 4th ed stat block. When the 3.P wizard casts a SoD, use the 3rd stat block for saves etc...