So your problem then is that they will be putting other publishers out of business? Other publishers who are presumably also not paying any rights at all for these orphan works (which they might well happily carry on distributing for all eternity and earning income from without putting a penny away should you turn up and claim your rights). My point here is that anyone else would have the same right to digitise and publish the same orphan works under the same system. Your concern over opt-out seems hollow. If you are the rights holder and object you opt-out, if you don't then you either aren't around, haven't noticed it yet or don't care. Opting-out means you get any money made that has been held in trust and retain your rights, they remove your work from distribution just as if it had been published without permission by anyone else and no financial harm is done, you just don't get any more income from that source and nobody can read it any more until you publish it yourself..
If they were claiming the exclusive rights to publish these orphan works by default then that would be different but as I understand it they aren't and it would seem ludicrous to do so - I can't believe even the Mighty G would be so arrogant and their own lawyers would certainly advise them they have no inherent right to do so under current legislation in any country I can think of. Digitising a work does not make you the owner of that work. At the moment it doesn't give you any rights at all and that is the only fundamental thing that would change. What it comes down to is they are trying to nudge the law along; to allow for anyone to exploit an orphan work unless permission is ultimately revoked and applying compensation in any such case. It does not seem to me an unreasonable change...so long as it is independantly monitored.
Obviously there are other details to be concerned about for rights holders such as; the fact that they have already started with no legal framework in place; the possibility that you might have intended your work to be entirely free and public domain; the chance that inappropriate advertising might accompany your work and you may wish to object to that if you later discover it - these things and many others spring to mind. But at the moment I can see litle difference between what they are proposing and the work that the MPRS does within the music industry. Clearly it requires oversight and regulation but let's face it that would never have happened at all if someone hadn't got the ball rolling and ultimately somebody surely has to start digitising all this stuff or it will simply be lost forever?