For a while new theory has been in short supply. So top plaudits are won by quality empirical work, but lots of people have good skills. There is thus a premium on a mix of clever ideas — often identification strategies — and access to quality data. Over time, let’s say that data become less scarce, as arguably has been the case in the field of history; for instance lots of economics researchers might have access to “Big Data.” Clever identification strategies won’t disappear, but they might become more commonplace.
We would then still need a standard for elevating some work as more important or higher quality than other work. Popularity of topic could play an increasingly large role over time, and that is how economics might become more trendy.