So much of this is taken into account with NPCs though. Since Gnomes and Halflings already exist in the game, it's a zero cost for making them work with armors and weapons for PCs, given they already work with NPCs.
If gnomes and halfings flat out didn't exist in their game, then it would mean a bit more.
As for dialogue checks and whatnot, based on my previous experiences with RPGs I would be very surprised if the amount of work done on these goes beyond the usual fluff. In other words, the work requirement is minimal.
Taking a look around this thread at Bioware, it seems like one of the many uses of the DM Client is to do on the fly testing of modules. But, this post by Patrick Mills is that these bug testing features will not require the DM Client and can still be done.
Initially it wasn't expected to be changed. Later, (I suspect after engine rewrites and whatnot), it apparently has. We don't even know that it hasn't been touched...just that it won't be finished. I'm sure other details were considered higher priority during development at various points in time.
A DM Client exists, but not one that works with NWN2.