1, said first conclusion
Express currently do not see the signs will be replaced by the koa2.
For now, Express ecological more mature, relatively low barriers to entry. But the highlight of koa2 attractive enough, ecology are starting to become perfect.
2, the threshold for the use of
From the use of it, Express is more better for beginners, facing the official website minor changes can do something to change it.
koa2 entry threshold higher than some Express, leaner kernel brings a small problem is, the higher the ability of building blocks of user requirements, even after all the core routing functions are removed.
Not to mention koa2 the most attractive async / await, many are beginners promise not understand, async / await with it a loss, koa2 one of the most essential part of it is of no use.
3, the trend is
After node expand community participation node server program students will be more and more. By then, the requirements for the server framework will be increasingly high, that time is a variety of enterprise-class solutions for their battlefield. The core is likely to still based Express or koa2, or other.
As Express and koa2, or will continue to have a large market, at that time I do not know how many versions.