i seriously doubt that there would be any difference between Libra and PayPal. in my view they are exactly the same thing and people (the end users) don't care or even notice what the underlying technology is, whether it is a simple database (aka PayPal) or a blockchain (aka Libra) in the end they will be having an account linked to their identity on a website controlled by a company that acts as their "online bank".
and i don't think they are going to put any kind of links between their coin and bitcoin, their website, their paper,... don't even mention bitcoin. not to mention that it will be centralized.
Libra is similar to what XRP is today, but then even more centralized. You will have your private keys, and you will be able to store your funds offline. PayPal does not offer you that in any shape or form. That's where Libra and financial institutions such as PayPal differ on a fundamental level.
As far as being linked to Bitcoin goes, that will happen through crypto exchanges where they already offer support for USDC, USDT, PAX, etc. Libra will be the next one to enter the list of stablecoins. It will help prop up Bitcoin's price and make sure capital stays within the system just like how capital in the aforementioned stablecoins stays within the system.