Does anyone know how long Salesforce will continue support for JB4A-SDK-Android v4.5.0? (Since currently the SDK is deprecated)
It would be best to reach out to SFMC support. SFMC support has access to backend team and they can provide you with the details you are looking for.
v4.5 of the SDK was released in July 2016. What is/is not supported really comes down to the customer ask. Features clearly won't be ported back that far, but if there were a critical bug found, that had not already been corrected with an updated version of the SDK, it would be discussed and prioritized accordingly.
Is there a specific reason you're not upgrading to, at least, v5.4.4?