The next release brings back support for more import formats, including v3 import formats. It also adds a few new ones:

This support will be added to Import as well as a new way to add links to collections or tabs to the current session.
Export formats will be expanded as well, though initially just to a subset of those listed above. This will be extended later to include all import formats and possibly HTML, Markdown, and others.
It's clear now that we didn't do a great job communicating the UI changes in v4, and especially WHY those changes were needed. We also should have better explained why it was necessary to drop features in the initial v4 release and that those gaps would be addressed in follow-up releases.
The situation was much more complicated than anyone not directly involved in SB development could possibly know. I won't go into detail here, but I assure you that SB v3 was far from perfect in terms of feature set, usability, reliability, and especially maintainability. These issues, along with impending Chrome deprecations (Manifest v2 and Web SQL Database) impacting major portions of the codebase, made the v4 rewrite an inevitability. Withholding a handful of features from the initial v4 release was necessary to meet the hard deadlines imposed by those deprecations. The alternative was that a significant percentage of users would end up losing their data.
Please understand that v4 was a huge leap forward in establishing the technical foundation required for continued growth. There are hundreds of feature and enhancement requests in the backlog, many of which would have been difficult or impossible to accommodate on the v3 codebase. v4 also included hundreds of user-facing improvements in the form of new features, enhancements, and bug fixes. Some of them are outlined in the
release notes.
Cheers,
Hans