So I'm actually about to replace my junky BSO with derailleur with a IGH bike for (mostly) this exact reason - better weather protection. I'd heard the Nexus series needs more lube when you first get it (which, thank you for reminding me, I need to go start a thread on). How can I better protect a IGH from daily winter (or in the greater sense, wet) riding? Where does most of the trouble enter the hub? Would a chain case (which I'm getting with the bike) help? The one I'm looking at uses grease instead of oil for...some reason...which I would think wouldn't "wash out" as easily (making salt/grit stay longer?) but better repelling water.
As to drive-train although the first impression of many people is to go for an IGH don't forget what happens to those when you get winter moisture especially with road salt inside of them and very few of them are adequately sealed to prevent this when subjected to the grind of true daily winter riding. Also don't forget that many IGH shift controls are also subject to icing up just like derailer systems. Then of course one should also realize that although a rear derailer is often unreliable at best in winter the same is not true for a front derailer which provided its control cable doesn't ice up in its housing is often extremely reliable in winter conditions. My solution thus has been to eliminate the rear derailer and instead rig up a simple and reliable chain tensioner that pulls up on the bottom of the chain loop in its middle and just shift the bike as a three speed using the front derailer only on the three front chain-rings. In most cases I've left the rear multi-sprocket spool in place and I can also change gears on the rear by stopping and manually moving the chain on the rear to a different sprocket if I so desire but the problems with the rear derailer icing up and even jamming up and seizing (been there done that) under winter riding conditions is eliminated.