1 Storage, short-Lithium & Calcium chemistry, and more batteries to be invented, 4 hour-ish; medium-flow batteries 4-24 hours-ish; pumped hydro 12 hours to 3 days. Weeks and months is in the research stage with a variety of ideas.
2 Customer load flexibility. In the US we are starting with 2-4 hours, called maybe 20 days a year. That can increase to year around. Your peak hours in 24 are usually about 4 hours.
3 More long distance large power lines as discussed in
https://www.nrel.gov/analysis/seams.html. Europe has the start of this and has transmitted hydro from Sweden and Norway to the South. There are also a good number of undersea cables for moving wind from the coasts. China has it. It is being discussed in East Asia.
4 Today hydrogen is in the hype phase, it will be at least 5 years to see what will be real.
Utilities do probabilistic 15 minute to hour-level simulations of their year in generation and load over their transmission topology for 20 years out. NREL does similar. To do the simulations, you have to specify a loss of load probability. It is not zero. The software is proprietary, the databases underlying it are proprietary, and the software is expensive. But some of those plans are public in the form of the utility Integrated Resource Plan in the US.
In batteries, the thing I would watch is the introduction and cost curve for calcium ion batteries, CATL is a maker. The other one is the Lockheed Martin longer duration flow battery.