What will happen if all 21 million bitcoins are mined?

People love spreading doom and gloom about falling hashrate as the block reward drops. I think it could be a positive for Bitcoin. In a few years from now bandwidth, storage and processing power are going to be so cheap and plentiful that it should be trivial for individuals to run full nodes on their personal devices. And these devices could be set to mine like the original bitcoin client. If we were to see a fall in asic mining and large mining pools being replaced by every user on the network being a solo miner then hashrate and network security would likely increase. As would decentralisation. Currently people are looking at tomorrows problems with todays technology. As long as devs and noderunners keep on top of things the network should be secure beyond the lifespans of everybody here.