Honestly I think Sigma's "art, sports" style of trying to break their line up is a foolish move because it attempts to impose a use or concept of use on a tool that, whilst it has generalist uses, can generally be used for anything.
That said new primes from them would be interesting, they've always made some good telephotos and zoom lenses in the long ranges and, provided that they put the money behind them, can make some very good quality options. It depends on if they are going to pitch the line more toward quality or price though and on what features will be missing if they go for price.
Tools of the trade: Canon 400D, Canon 7D, Canon 70-200mm f2.8 IS L M2, Sigma 120-300mm f2.8 OS, Canon MPE 65mm f2.8 macro, Sigma 150mm f2.8 macro, Tamron 24-70mm f2.4, Sigma 70mm f2.8 macro, Sigma 8-16mm f4.5-5.6, Raynox DCR 250, loads of teleconverters and a flashy thingy too
My flickr