The core work is done, yes, draft-ietf-jmap-core-17 and draft-ietf-jmap-mail-16 [edit: fixed draft name] are in the RFC editor's queue, how long it takes to get through that queue can depend on a lot of variables. At the end it goes to "AUTH48" which is notionally 48 hours long but a few weeks is more likely in practice, and then it gets cut a number and becomes an RFC.
The Working Group still has open items, including calendaring (because people never can build a mail system that doesn't involve calendaring for some reason), handling "read receipt" type features and because this is Current Year a mechanism to involve WebSockets. Either those will eventually also be polished into standards, or they'll be abandoned at some point and undelivered.
Should we take this IETF blog post as an indication that the standardization work is almost done?