This page contains an overview of some of the key proposals for Jenkins 2.0.
Below are a list of the blog posts summarizing the proposals, with their associated issue tracker links where you can provide more feedback:
Introducing a policy for API deprecation (JENKINS-31035)
Splitting Groovy out of core (JENKINS-29068)
core
Pipeline as code front and center (JENKINS-31152)
User experience improvements (part one) (JENKINS-31156)
Improved "Out of the box" user experience (JENKINS-31157)