The older switches are still supported. They just can't run v15.4 and higher.
There are some implications to that that you should be aware of:
- If you need to implement a feature that is available in one of the newer versions of EXOS (more than one MLAG neighbor, for example), you can't have it in the old hardware.
- As new models come out, it won't be possible to stack them with older switches because all switches in a stack must run the same image version and there old ones won't support the newer version required by the new swich.
So while your old switches may have a happy long life ahead (I visit many customers still running v12.0 in their switches with no intention or need to upgrade them), you may want to start planning their replacement if your network environment is demanding and requires state of the art features.
Regarding the 8900 modules, sorry, I missed those. That's a mistake too. Those modules are 'alive and kicking' and have no limitations regarding maximum EXOS versions... They are not obsolete and have no announced End of Sale date, so you should not worry.