I wondered the same thing and got some real good support to say the truck would be a good platform. I have a 99 extended cab with the 5.2mag, a suspension and body lift and 33's( look at my profile picture) and between me and my friends 2 kids ageing between 9 and 12, the truck works perfectly, the kids have enough room to be comfortable in the back seats and I believe my truck has more payload then the newer ones due to the bigger motor and the same drive train as a ram 1500 ( towed a couple cars and never felt them behind me). Though I have yet to take it out on a full expedition run I have taken it out on a couple mud trails and trust me when I say its got plenty of power, as it sits I get between 17 and 18 if I get the cruse set right. All in all it can serve well for a dual purpose rig.
The biggest down side for me is the fact that all Dakotas and Durango's of all years do not have very good off road support with parts, very little available for these truck so depending on what you want chances are it will have to be custom, however you did mention you wanted to get one and do a axle swap, that is the best move you can do with these truck and the axles from a 2005-present F250 super duty will fit under the wheel wells so no worried about the wheels being wider then the truck. Just find a good fab shop that is willing to work with you, that shop I am going to is charging me $4500 to do the whole thing meaning getting the axles, doing the full suspension front and back, all the linkages and a 4 link set up. Once all that is done then the payload can increase a little from there since the super duty suspension would be used on it.
