I understand your point, but gmail labels are such a good idea that Thunderbird should implement them as a native feature (even perhaps proposing it as extension of IMAP standard).

Also think Thunderbird should implement JMAP (Fastmail standard) and/or Google RESTful gmail API because these are open standards worth supporting.

Another feature that I would like to see more fully supported in Thunderbird (through better synchronization with mail provider server back-end) is editing emails, to include most importantly the ability to remove bulky attachments without losing email text or touching important meta-data. Unfortunately gmail treats each email as an immutable object, and the hacks that have been suggested to date to work around this limitation have all been clunky at best.