It's a theoretical solution because developing software to install a digital lock costs money. These aren't big producers. The performer in this case isn't necessarily always the producer. The performer can't afford to do it, unlike the producer who can.
Furthermore, you know that the major sound recording producers have abandoned the digital lock model. I'd simply like to emphasize that for every digital lock there is a key. From the moment there is a key, creators can allow copies to be made, which will be distributed over the Internet.
So the solution, in the field of copyright in general and even in the book sector, is to provide access to works. That's the solution that has been selected. On the other hand, the idea is to provide for a right to compensation, which grants access to works and enables creators to be compensated.
The digital lock route is therefore a dead end street for us and one that the major producers have even abandoned. Consider the example of iTunes and Sony, which have decided to remove digital locks from their CDs and downloads to permit wider distribution in response to consumer dissatisfaction.