You can tour on an IGH, IMHO if you don't abuse them they will last just as long or longer than the dérailleur system. Most of the ones that I have seen are not intended for 500# cargo carts, because the extremely low gearing required will toast the internals by putting too much strain on them. The Dutch use the Shimano 8 speed on a Bakfiets and they aren't a lightweight machine by any stretch of the imagination.

Aaron