Will there be more or less volcanic activity in the future?
If I knew the answer to that, I could also tell you what the stock market will be doing this time next year! I predict we will have more of the same, which means I don't think there will be an increase nor a decrease in volcanic activity worldwide. I think we have a better understanding now of why volcanic activity occurs in some parts of the world, moreso than others. Volcanic activity seems to be just as natural a process to the Earth as perspiring would be to a person when their body temperature rises. Harry Hess provided an interesting mechanism when he discovered the underwater mountain ranges, where new ocean floor was being manufactured. Later discoveries found ocean trenches where the old ocean floor was being subducted and recycled. I think this cycle of sea-floor spreading, of volcanic activity around the Ring of Fire, is a natural, somewhat predictable phenomenon that will continue as long as the Earth maintains its existence in our solar system.