Named Credential: Authentication process and refresh token

Currently, Named Credential refreshes access token only if Refresh token was provided otherwise not. Recently, I got stuck with same issue while developing integration with Instagram and I had to opt the custom solution by using custom setting and Visualforce page.

Actually, Salesforce is following a standard option to refresh the token, they can not provide a customized URL/option to refresh it for each external system....if each system has it's own syntax to refresh token then how Salesforce would handle that for each individual system.