The Lav-25 half-track is particularly credible, given that the LAV steers on it's front two pairs of wheels. It would be even better if the drive sprocket was at the front, thereby shortening and simplifying the drivetrain.
The 4x wheels + 2x tracks paradigm gets me wondering. Imagine if the four wheels were at the corners of the vehicle and the tracks in the middle. The wheels would give you the 'lift' neccessary to get over obstacles, which in turn would mean that the tracks' front and rear sprockets wouldn't need to be raised. that would give you more track contact area on the ground. You could put the drive sprocket above the centre of the track, the latter then having a triangular shape, and that would enable you to have it pivot freely around the drive sprocket axle liek the 'walking beam' suspension on the back of ENGASA AFVs and trucks.