EU referendum and US elections yes, the rest, no.
It will not be the first time a party leader and party has stood or fallen on the May local elections. It hasn't been game changing in the past and isn't going to be in 2016. I think a lot of the drama over Jeremy Corbyn's leadership, is grossly overblown. His situation is not unique. The main problem with all our political parties is the dearth of credible leaders. I am sure the reason Jeremy Corbyn got in was because of the complete lack of charisma or obvious leadership credentials in any of the other contenders for the job.
Trident will be turbulent but not game changing, Remember the cancellation of the TSR2 by Jum Callaghan in 1965? A far more catstrophic decision, but no game changer. ditto expansion at Heathrow. Just the ordinary contentious issues that will probably include resignations that governments have to make decisions about, but not game changers. I think that would also apply to the junior doctor's strike that you mention Durhamjen
What would I add? The political situation in the arab world, not just the middle east, A catastrophe in Syria, especially if the US and Russia are either driven apart as a result or start pulling very firmly together, could be a real game changer, likewise Libya