The argument that important ML algorithms should be highly scalable ( O(logN), O(N), O(NlogN) ) holds in fields that are rich in "big data," with millions to trillions of data points.

However, there are also many fields where acquiring a large ( > 100s-1000s of samples) is infeasible. This is especially relevant in medicine and biology. Many applications are constrained by small sample sizes and may have a feature count that is orders of magnitude larger than the sample count. Examples include fMRI studies and gene expression studies. Don't discount research in methodologies (such as SVMs and many graphical models) that have superlinear performance as impractical for real-world applications, because these are used heavily in certain fields.