Yes, whenever that Thunderbird transition actually happens! I use Thunderbird on desktop, so I'm looking forward to seeing how that goes, but it's been a long time since it was announced, and is there even a date established?
More likely it’s an attempt to get the preview text a lot of mailboxes show to not show extra content.
Meaning they want you to see “terms and conditions updates lulumon” and not “terms and conditions updates lulumon hello there isVeryLoud, we have upd…”