What about supporting older 32-bit applications? Without 32-bit support, there won't be any way to run 32-bit games in Wine for example, unless Wine will somehow rewrite it all to work with underlying 64-bit libraries.
That's good! Though since the focus on 32-bit will decrease, it's possible that support for it in libraries will start deteriorating, and in the long term it can become an issue for use cases like Wine.