Can the plugin create Direct Debit Payments? I know it does recurring payments, but I believe that DD's are a different process
You mean SEPA Direct Debit? Yes and no. It's implemented, but disabled at this time as their test credentials don't work so I can't confirm if our implementation is working or not. If you mean Debit Cards then yes as that's just a Cards payment source.
I assume that taking Bitcoins would be a Stripe issue and have no direct ramifications on CB.
Correct.
If I wanted use Stripe to take cards, DD's and Bitcoin, but wanted to show them as different options on the subscription screen is this possible?
Yes, set "Payment Button method" to "Inline Form (Elements)" (default) or "Inline Form (Server Side)" then select the payment methods you want to support for "Accepted credit cards". Each will display its own button.
Would I duplicate the plugin and just rename/separately install them?
You'd never have to duplicate the plugin. You'd just make another Stripe gateway in CBSubs if this was the case.