As the Lifecycle page on the Jetson Developer Zone, we will have official EOL notice be sent a minimum of 8 months prior to the last shipment for customer to do the preparation ahead.
The L4T sustaining releases for Jetson Nano will continue to be made as deemed necessary. You can refer to our last EOL notice for Jetson TX1, and the support for Jetson TX1 is still continuing.
We can’t disclose the plan for OS upgrade and kernel version, however you can refer to Jetson Roadmap webpag to get some ideas.