Mobile is often said to be an inherently worse display advertising environment than desktop. Which would mean that mobile long-term is a worse platform for publishers who sell advertising as monetization will be lower.
I'm not convinced that is true longer term. Apart from being sad, given the poor state of online advertising, I'm not sure it will be true.
The small screen often gives an ad 100 % of the screen real estate, which is a better experience and gives higher impact. A user will probably look at it only for a few seconds, but the same is true for desktop web.
In addition to the medium's inherent qualities, publishers need to sell and advertisers and agencies need to be ready to buy. Both usually take a few years to become reality. So I actually believe mobile will be better than ok as a display advertising medium.