Hawaii has a 100% RPS by 2040. They are making a lot of progress towards that and will become a great case study not only for other islands and isolated locales (eg. rural Alaska), but distributed generation will gradually overtake utility-scale plants, thus reducing the importance of the transmission infrastructure.
Coal has no future and will continue to decline. Plants are closing due to economics, alone, which is why there are no new coal plants in most parts of the country. Gas will definitely continue to overtake it in the short-term, but eventually their growth will stagnate while wind and solar continue to grow. How soon this happens will largely depend on the volatility and overall direction of gas prices.... This legal case by Sunniva and Solarworld to impose tariffs on solar panels, could definitely be an issue, but only a short term one.
As for overall energy usage, electrification (as well as automation) of transportation and other sectors will result in the gradual decline of oil, as well. There's been too much production for awhile, which is what's causing the low prices and high inventories. That's not a viable long-term solution.