I'm working on an analysis of the field but here it is. The big development from a US perspective is that Olympic medallist Sally Kipyego is now officially running for the US and is in the field.
Update: Our analysis is done and the link appears below
2019 Boston Marathon John Hancock Elite Men's Open Field
Lawrence Cherono Kenya 2:04:06 (Amsterdam, 2018)
Sisay Lemma Ethiopia 2:04:08 (Dubai, 2018)
Lemi Berhanu Ethiopia 2:04:33 (Dubai, 2016)
Solomon Deksisa Ethiopia 2:04:40 (Amsterdam, 2018)
Lelisa Desisa Ethiopia 2:04:45 (Dubai, 2013)
Kenneth Kipkemoi Kenya 2:05:44 (Rotterdam, 2018)
Felix Kandie Kenya 2:06:03 (Seoul, 2017)
Geoffrey Kirui Kenya 2:06:27 (Amsterdam, 2016)
Festus Talam Kenya 2:06:13 (Eindhoven, 2017)
Wesley Korir Kenya 2:06:13 (Chicago, 2012)
Philemon Rono Kenya 2:06:52 (Toronto, 2017)
Hiroto Inoue Japan 2:06:54 (Tokyo, 2018)
Benson Kipruto Kenya 2:07:11 (Seoul, 2018)
Ghirmay Ghebreslassie Eritrea 2:07:46 (London, 2016)
Dathan Ritzenhein USA 2:07:47 (Chicago, 2012)
Yuki Kawauchi Japan 2:08:14 (Seoul, 2013)
Zersenay Tadese Eritrea 2:08:46 (Berlin, 2018)
Abdi Abdirahman USA 2:08:56 (Chicago, 2006)
Mohamed Reda Morocco 2:09:16 (Chicago, 2018)
El Aaraby
Hayato Sonoda Japan 2:09:34 (Oita, 2018)
Scott Overall Great Britain 2:10:55 (Berlin, 2011)
Jeffrey Eggleston USA 2:10:52 (Gold Coast, 2014)
Jared Ward USA 2:11:30 (Rio de Janeiro, 2016)
Elkanah Kibet USA 2:11:31 (Chicago, 2015)
Timothy Ritchie USA 2:11:56 (Sacramento, 2017)
Shadrack Biwott USA 2:12:01 (New York City, 2016)
Scott Fauble USA 2:12:28 (New York City, 2018)
Aaron Braun USA 2:12:54 (Houston, 2015)
Brian Shrader USA 2:13:31 (Sacramento, 2018)
2019 Boston Marathon John Hancock Elite Women's Open Field
Aselefech Mergia Ethiopia 2:19:31 (Dubai, 2012)
Edna Kiplagat Kenya 2:19:50 (London, 2012)
Mare Dibaba Ethiopia 2:19:52 (Dubai, 2012)
Worknesh Degefa Ethiopia 2:19:53 (Dubai, 2018)
Meskerem Assefa Ethiopia 2:20:36 (Frankfurt, 2018)
Jordan Hasay USA 2:20:57 (Chicago, 2017)
Belaynesh Oljira Ethiopia 2:21:53 (Frankfurt, 2018)
Sharon Cherop Kenya 2:22:28 (Berlin, 2013)
Desiree Linden USA 2:22:38 (Boston, 2011)
Marta Megra Ethiopia 2:22:35 (Toronto, 2018)
Betsy Saina Kenya 2:22:56 (Paris, 2018)
Caroline Rotich Kenya 2:23:22 (Chicago, 2012)
Sara Hall USA 2:26:20 (Ottawa, 2018)
Eva Vrabcova Czech Republic 2:26:31 (Berlin, 2018) NR
Sally Kipyego USA 2:28:01 (New York City, 2016)
Krista Duchene Canada 2:28:32 (Toronto, 2013)
Alyson Dixon Great Britain 2:29:06 (London, 2017)
Lindsay Flanagan USA 2:29:25 (Frankfurt, 2018)
Becky Wade USA 2:30:41 (Sacramento, 2013)
Sarah Crouch USA 2:32:27 (Chicago, 2018)
Sarah Sellers USA 2:36:37 (New York City, 2018)
Mary Wacera Kenya 66:29 (Houston, 2016)
http://www.letsrun.com/news/2019/01/john-hancock-announces-2019-boston-marathon-elite-field/