Not sure about 1 and 2, but I'd think that 3 and 4 surely aren't acceptable, as they obviously undermine the purposes of sealed bidding on ebay and sniping here, respectively. For example, it seems to me your suggestion 3 cannot avoid giving away the max bid of winning bidders (and everyone can see who that is) for the items. Yes, that is valuable information from one point of view--but it seems to me such a feature would unquestionably complicate and distort the whole bidding system (introducting uncomfortable strategic considerations when otherwise one could live happily on the simple "just bid the most you're willing to pay" rule), tend to inflate bidding, and change the world as we know it for the worse, and I doubt that any ebay bidder out there who has had some measure of success would find it palatable. Or consider for a second your suggestion 4: For example, if it were implemented, and I bid the $250 and got this message, why should I not place another snipe for $300? (My snipes are not binding after all, I can cancel them at any time.) And keep upping my snipe. Eventually, under your scheme, I would cease to get a warning message from AS--and then I would know what the highest snipe had been! Thus the suggestion would defeat the very purpose of placing a snipe in the first place. This example just scrapes the tip of the iceberg of the reasons for objecting to the suggestions. Seems to me the whole system would become a wreck.
Relating to suggestion 2, there are some useful resources at toolhaus.org , though perhaps not exactly what your suggestion 2 points to.