It must be. Otherwise, the network won't have a future. It can't survive on good will, and the incentive structure rewards routing when demand for "small" bitcoin payments go up.

But I guess it will take a similar path to that of bitcoin mining. As the routing market is terribly competitive, big and extremely professional players will arise and take most of the game. Think of nodes with perfect uptime and latency, large amount of capital, extremely well thought channel choices and active channel management. They will only grab a tiny percentage of what they route, but they will route so much that it will be enough income to sustain themselves.

The good news for all of us is that this could mean unbelievably low fees for sending payments over lightning. Think about it: a serious, professional operation such as the one I described only takes a handful of professionals to be run. And these don't even need to be software engineers from the Bay area that cost hundreds of thousands. So maybe a team in Romania could run this with a total cost below 200,000$ per year, while their node routes several billion per year. So fees would be lower than 0.001%.

This is a very mature future I am imagining though. There might be some decent money to be made in a more amateur-ish way for the next months or years. Look at zero fee routing for example. The node is a single man operation, but he is having significant income.