It's a good question because we don't yet know what Sigma's new strategic roadmap looks like in terms of product launches or relaunches. My expectation is that:
a) genuinely new products will conform to the new design protocol we've seen with the three lenses announced, and;
b) Sigma will upgrade most or all of its "modern" existing lenses (50mm included) in the way that has already been announced for the 17-70mm and 120-300mm zooms.
If the second point is correct, the questions then are, how quickly and with what price increase?
Concerning timescale, there will be many informed buyers like you who know about the new designs and who will be holding off buying existing Sigma products because of the expectation of an upgraded version. This obviously won't be good for Sigma so it will be in their interests to roll out their upgrades quickly or otherwise to tell us that an upgrade for a particular lens is not planned. Needless to say, re-engineering many products would be a huge undertaking so a timescale for any given lens upgrade is anyone's guess.
Concerning price, we'll have a better steer on that when prices are announced for the 17-70mm and 120-300mm.