I think I can see three eras of Warhammer commonly played: The Ninth Age, the 8th ed, and Oldhammer.
The Ninth Age is a competitive scene, where people are concerned with the rules and balance. You would need to make the Halfling book competitively interesting, and you would need to give Halflings a game role different from all the other armies, if you want them to use it.
The 8th ed is perhaps mostly concerned with keeping the Old World alive and enjoying GW models in that setting. I would think there are 8th ed players who would eagerly welcome a concice Halfling book. Then again many 8th ed players may not have any Halfling models, and might not have the time/money/interest to buy them.
Oldhammer has a combination of nostalgia, appreciation of older figures, appreciation for the relaxed spirit of the rules, and of course the Old World setting. They are usually people who will go for editions which did have Halflings represented, so will already have access to some Halfling rules, and likely models too. Maybe they are the ones who would like to have the concise rules for a Halfling army. Problem is, you have 3rd to 6th editions, and each plays a different one.
-Z