Sigma did reintroduce the 120-300 F/2.8 and that didn't quite need an update, they just bumped it up with the new design, likely with no optical difference. But, since 35 is the other 'normal' and too close in application to the 50 I think Sigma went for getting good reviews with the 35 to then move forward with the new reputation and would introduce another 50mm. I don't think we'll see an update soon though, and the 85 1.4 is great so they might bring back some of their fast wide primes eventually?
Yes, I hope we'll see new fast wide primes from Sigma too.
The new design would benefit all of their lenses - user-selectable focusing speed, min/max focus distance, lens-based AFMA, materials resistant to heat-expansion, etc. Since this is all central to Sigma's new strategy, we can be sure they won't stop at what's been announced so far. Which lenses they re-engineer, and when, remains to be seen but I would have thought the 50mm and 85mm would be among the first candidates.