The Spring '19 version of the Lightning Experience roadmap is now live. See what's slated for the next release and beyond! The PDF version is here: https://www.salesforce.com/content/dam/web/en_us/www/documents/e-books/salesforce-lightning-roadmap.pdf.

Or check out the Help & Training version, with complete history of released features: https://help.salesforce.com/articleView?id=lex_roadmap.htm.

We've also updated the Lightning Components roadmap: https://help.salesforce.com/articleView?id=lightning_components_roadmap.htm.