I don't understand what these unconfirmed transaction actually imply.
That the value of BTC is (artificially) lower than in reality?
Or on the contrary, that BCH value will again increase after the transaction are confirmed?

Just means that the transaction has been started but because computer power is lower (gone over to mining BCH) it is taking longer for the transactions to get in a block and join the chain. Once it is on the chain, it is considered permanent and you can't do anything about it - it is confirmed - It is considered that 6 confirmations (6 added blocks after your transaction has been added) means that no group could undo the chain and is safe for big $ transfers.