September 4th is the official Ceneri opening, timetable traffic is due to start December 13th
Zug to Arth Goldau is due to re-open on the same date. The new double track section starts at Walchwill station 9+452 and goes to about 11+150 (Zero is Zug station and Arth Goldau is 15+758)
The new Bözberg tunnel is also expected to open 13.12
Also due to open in the next few months:
26.09.2020 deviation through new Boll station on Bern-Worb line (RBS)
October ? LEB new tunnel section at Chauderon in Lausanne
13.12.2020 TPG Geneva tram extension Bernex to Vaiily
I don't think the extensions to the Ceneri and Zimmerberg tunnels have got beyond the proposal stage though with Zimmerberg the Junction layout at the Thalwil end was built with the tunnel so that any new construction can easily be joined to it.