Last week the feature plugin decision deadline closed and WordPress core contributors approved Responsive Preview and Selective Refresh for merge. The merge deadline is Wednesday, February 17, followed by the first beta next week.
According to the meeting summary written by 4.5 release deputy Adam Silverstein, the most important question to answer is whether widgets should opt-in for selective refresh by default. Weston Ruter recommended that they require opt-in for widget selective refresh in 4.5 and warn developers that it will be set to default in the next release.
The new responsive preview feature is part of the Customizer UI Experiments plugin. It adds buttons to the customizer controls footer which allow users to preview site responsiveness while making changes. The buttons have icons for desktop, tablet, and phone-sized devices with portrait orientation.
According to Silverstein’s summary of last week’s meeting, WordPress 4.5 will not ship with WP REST API endpoints as previously planned:
The REST API team’s proposal is to merge the four main endpoints when they are ready, and they are not ready for 4.5. As such, no endpoints are targeted for WordPress 4.5.