User blog comment:Rappy 4187/Technical Update: November 23, 2016/@comment-5211495-20161125141538/@comment-26339491-20161128180017

They coexist for now, but eventually, the forums will have to be closed and their content migrated to Discussions. The reason for that is that, when the forums were first built, the engineers at the time made some architectural decisions that now make it incredibly difficult for us to fix some of the biggest issues the forums have, namely inaccessibility from search, lack of mobile compatibility, and a number of other issues that users don't necessarily see.

To truly address these problems we have to rebuild the forums from scratch, which is what we're doing with Discussions. This means that, once Discussions has replaced the forums, our engineers will have to spend much less time on fixing tricky forum bugs, we'll have a (hopefully) even better conversation platform that the forums were, and we can spend more time and resources on improving other parts of the site, and adding other new features.