To be fair, Sisters have never had a huge amount of love from Games Workshop. Their model range has pretty much stayed the same or shrunk over the last decade or so. That, the one pose models, the ever present threat of being 'squatted', no new models and the expense of them puts people off (including me). The actual Sisters models are AWESOME and the new Saint Celestine is a very nice model. But the old metals are currently putting me off.
I think if Sisters ever got a re-do they'd be done by a LOT of veteran players and newbies alike.