International Law
eBorders is contrary to International Law for seagoing vessels, which applies to recreational boaters; eBorders says a skipper must register your crew and ports of entry/exit 24h in advance, and then do what you registered to say you would. Even if a storm brews up or you have an equipment failure, or someone gets ill, or similar. The International Law of the Sea states a skipper must do what's right for safety of all aboard and other vessels, including changing plans, going later instead, going to a different port because of weather and so on.
I imagine the same applies to recreational aviation. Bad weather? Sorry, you must land where you said you would - even though the CAA will prosecute you for trying in that fog.
And of course, people making illicit journeys simply won't register, so it'll make no difference to them at all.
I guess TPTB have looked at the amount of traffic from Eire to UK and realized it's impractical; lets hope they realise the same applies to near-Europe too, soon.