East Asia is uniquely different from other regions, there are only a handful of nations, essentially is all about three big nations, each being the 1st, the 3rd and the 5th most industrialized countries in the world. While Japan and SK are well developed advanced economies of large (JP) to medium (SK) scale, continental-sized China is still developing rapidly.
The progress of economic integration isn't news, it is already happening on a daily basis, milestones like the CN-HK CEPA, and the recent CN-SK FTA, are just pragmatic solidification of ground realities. Despite the talks on CN-JP-SK trilateral FTA is still ongoing, some sort of compromise is likely to be made eventually. Economic integration is not just a political slogan that sounds flashy, but it's a momentum driven by business pragmatism.
The union of East Asia is in the making, purely in economic terms, and to a large degree "re-union" in cultural interaction between China, Japan, Korea, Taiwan, Hong Kong, Macau and even Singapore (though geographically they aren't in East Asia).
Political union of East Asia is a big uncertainty, or put it positively speaking a challenging opportunity. First of all do we see other so-called union that function well in politics? Say ASEAN, EU, Arab Union, African Union? It isn't easy as that's the nature of politics i.e. self-interests, security, nationalism. Not to mention China, central to East Asia, has a very different politico-social system which is highly suspicious by others. However it seems domestic reforms in China are going in the right direction, but it will take time and a lot more courageous efforts. Politics are won or lost in hearts and minds of people, being bigger than rest of the region combined, China should take the initiative in pursuing this opportunity.