A recent FCC listing for RM-846 aka Lumia 620 reveals that Nokia plans to upgrade its software, which may indicate upcoming GDR2+Amber update. Nokia mentions that, they are planning to bring Bluetooth low-energy to the device, which means upgrade to Bluetooth 4.0 from existing BT 3.0 specs of Lumia 620.
Actually if you remember all the Lumia WP8 were having BT 4.0 compliant chips from start, but due to WP8 restrictions limited to BT 3.0. Now, Nokia mentions that
With this application we are asking permission to upgrade devices FCCID:PDNRM-846 in the field with a software upgrade. We are upgrading devices with Bluetooth Low Energy (2402-2480 MHz).
The Bluetooth chip has been compliant with the Bluetooth specification 4.0 all the time but thus far the features have been limited by SW to use only BT3.0 features.
Now, if Lumia 620 gets an upgrade from BT 3.0 to BT 4.0 with next update which looks like Amber update from description of the update given by Nokia in application.
Nokia owns the product configuration. Nokia is building the product configuration. Deliveries from hardware and software providers are used. All software is delivered to Nokia. Nokia and Microsoft are responsible for packaging and delivery of the software. Nokia delivers the original product configuration, while updates hereto are distributed to the end user by Microsoft, using their software update servers.
Then it looks certain that other Lumia WP8 devices will also get updated to BT 4.0 with coming Amber update.