I just got the letter for my Explorer: no mention of doubling the existing points balance, which makes sense (since Gateway stashes would end up being more valuable post-deval).
Interestingly, the letter mentions a new benefit - the 'Hotel Collection' - which seems to be different to the Fine Hotels & Resorts Program. The benefit is that bookings of 2 or more nights through their portal entitles you to a space-available room upgrade at check-in and a USD $75 credit. Interesting, and useful, but I'll take a doubling of my points, thanks.
No word on Plat Edge yet - the Explorer letter mentioned that you'll get a letter for each Amex you hold. There is still hope, as my Explorer earns Ascent points, not Gateway. Fingers still crossed. If the Edge also doesn't get anything, then the Plat Charge guys can have some validation for their $1400 annual fee