I am thinking of selling my BB and pedal, Will the purchased song packs and drum kits be transferable to the purchaser?
Only if you leave them on the SD card. If you don’t want to sell them, it is easy to wipe the SD card and set up the default drum kits on it.
If the intent is to market the pedal with the transferability of the account (to download future updates—if and when they’re made), there’s nothing stated on the Premium link about transferability https://library.mybeatbuddy.com/terms-and-conditions/
The seller could e-mail firstname.lastname@example.org and ask.
What’s the likelihood of any future updates to the drum sets? No clue so my suggestion would be to make sure that you’ve downloaded and provided the latest premium kits for the buyer. The updated kits have been out for about a year and a half so if the seller bought his content longer than two years ago, probably a good idea to download the kits, import them with the BBM, activate them in the drum sets tab, save the project and synchronize with the SD card.