Great points. One of my motivations for an IGH isn't just the replacement of a derailleur, but also to recapture the advantages of the single speed. These include going back to a non-derailleur type chain that doesn't expect to be flexed laterally, and changing over to the deeper-tooth style chains rings and cogs that by their very design prevent derailment. I think the whole package results in longer chain life, and is characterized by lower maintenance costs overall, whether you measure those costs in monetary terms, time, aggravation or whatever. I guess what I'm trying to say is I wouldn't convert to an IGH and then continue to use derailleur type hardware, including the chain.