Maintenance for the week of April 6:
• [IN PROGRESS] ESO Store and Account System for maintenance – April 9, 9:00AM EDT (13:00 UTC) - 6:00PM EDT (22:00 UTC)
I don't believe it. Which is weird, cause I usually trust in Zeni.
I honestly expect we'll see this specific feature for sale again at some point in the future.
They could always skirt around the issue by... including it as another pre-order bonus, or adding it with a new purchasable bundle of features. Technically they wouldn't be made liars for saying that the Explorer's Pack won't be available again.