Exclusivity for certain buyers online i think will be unlikely, the vendors are watching closely and will be in no mood for cars coming up £short due to a limited audience, some vendors are already looking to dispose of stock elsewhere and the auctions know that achieving the expected returns for vendors in the next few months is crucial , so expect the likes of bca and manheim to drop their guard and allow jo-po to buy online too, they are well aware that the multi vendor crap is reliant on a certain customer so a change in rules is inevitable.
As for actually being at an auction, don't be surprised if certain group / supermarket buyers get an invite to attend pre-sale to inspect stock and leave bids, the ones that hoover up in volume the better stuff at the better sales.