I´d like to be able to simply save the pdf backup on my sdcard in order to manually transfer it to my pc.
Is that going to be an option?
yes, it will be in one of the next releases. hours after release this is already one of the more frequent requests.
Until the feature is implemented, you can try installing the Save to Phone app. It provides a Share destination which simply saves the shared data to a file on your phone. Works with Mycelium and any other application with a Share action. I used this myself to transfer the backup .pdf to my PC. Hard to believe this isn't built in to Android...