Currently BotPasswords feature allows generating a separate login for a bot and assigning a subset of the parent account's rights to it. This works great for a scenario when the owner of the bot shares their account with the bot itself. As far as I understand, that was the targeted scenario behind the current BotPasswords design.
However, I believe this is not a common scenario at all. Whenever a bot needs to have special rights, a much more common scenario is usually involved: a separate account is created for the bot and wiki administrators assign proper rights to it (e.g. a right to roll back or to stabilise the pages via FlaggedRevs extension).
This common use case is not very well supported by the current implementation of BotPasswords. Namely, there is no way to allow a bot to log in with full rights it was granted, because a lot of special rights are missing from the grants listed on the BotPassword page. For example, look at T150231: my bot can no longer stabilise articles because there's currently no way to grant `stablesettings` right to it since it's currently not included in any of the existing grants.
Thus, my proposal is to include another option on the BotPasswords page to allow the new generated account inherit all the rights granted to the parent account. This would support the wide-spread 'bot has a separate account' practice really well, gives a quick solution to issues similar to T150231, and otherwise looks a lot more logical for bot-only accounts.