Bookmarks (a.k.a Quick Links)
Use "Mail > Go to > Add Bookmark..." to save frequent searches or links to individual messages in Gmail. You can then navigate to those bookmarks via "Mail > Go to > Navigate...". It's intended as replacement for the retiring Quick Links lab feature.
Quote Selected Text
Gmail did also retire the Quote Selected Text lab feature. We went ahead and built a replacement for it. Simply select text in Mailplane and press either "Mail > Reply" (⌘-R) or "Mail > Reply All" (⌥-⌘-R).
macOS 10.13 Beta (High Sierra)
Apple made macOS 10.13 Beta available via their Beta Software Program. This update will allow you to start Mailplane on macOS 10.13 Beta. There are no other known issues so far but full compatibility is still being verified. Let us know if you run into any issues.