Tough question. I could never have imagined how much it has grown in just 3 years from zero so I would guess the coming 5 years would surprise me similarly.

People always asks me "But why do you still have to work on Mempool, isn't it finished?" but yet we continue cranking out new features, networks and we have already started to support more second layer networks. A guess is that the whole Lightning ecosystem will grow a lot the coming 5 years and supporting that in various ways will be a big task ahead.