Technically, you always play enchantments face down. but you can immediately pay the reveal cost and flip it over with no intervening steps for the opponent mage the chance to respond; no matter where they are on the board or what spells they have in hand or bound to their Mage Wand.
so, what I believe Rumsey is advocating is a kind of short-hand to just pay the whole cost and play the enchantment face up.
I think what is clouding the issue for Jon's argument is the whole two copies of Mage Wand thing. Disregard that in his 2 scenarios above:
for Scenario 1 assume that player B only has a Mage Wand with Seeking Dispel.
-and-
for Scenario 2 assume that player B only has a Mage Wand with Seeking Dispel and stipulate that he has a Dispel in hand.
In Scenario 1 the steps Jon describes are correct.
In Scenario 2 the steps Jon describes are correct with the exception that it doesn't matter that Sacred Ground was cast face down out of range from Player B, It could have been in the zone right next to him and Player B would still not be able to do anything if Player A decides to immediately reveal Sacred Ground.
in Jon's write-up at the end of the two scenarios:
"What I was talking about with "events" applies to Scenario 1. If the creature that has Decoy on it starts its move action, Player B can't use Seeking Dispel until the creature action is completed. This applies particularly for curses like Chains of Agony, where creatures take damage for every move action. Because Sacred Ground does not work that way, and because Player A in Scenario 2 chose to reveal it before Player B moved into range to use Seeking Dispel, that is not allowed."
Jon is correct that "if the creature that has Decoy on it starts its move action, Player B can't use Seeking Dispel until the creature action is completed." Player B does however have an opportunity to use his quickcast action immediately BEFORE or after he activates a friendly creature, so he could Dispel something like Chains of Agony before the creature moves.
In the case of Sacred Ground (sounds like a Sherlock Holmes novel), again, it does not matter that Player B was out of range before Player A revealed it, provided that Player A reveals Sacred Ground immediately after casting it. there is no intervening step for Player B to respond. If, on the other hand, Player A chose not to immediately reveal Sacred Ground, then Player B could use a quick action to cast Seeking Dispel.
I hope I am being fair to both sides of the discussion and that I accurately represented what you are each trying to say and that the corrections that I offered don't come across as antagonistic in some way.
hope this helps.
p.s., you can only have One copy of Mage Wand equipped at a time.