UPDATE: On 23 August 2017, the following text was added to the original 10 July 2017 post on ScoutingMagazine.org:
The National Boy Scouting Subcommittee has released this statement, saying that the policy outlined in the post below has not changed but is currently under review:
"The current policy regarding Eagle Palms is any Eagle candidate having a board of review on or after Aug. 1, 2017, is eligible to receive the appropriate number of Palms based on the total number of merit badges earned prior to his board of review. However, due to concerns from the Scouting family, this policy is currently under review. All points of view are being carefully, respectfully, and thoughtfully considered. However, that does not guarantee that any changes will be made to the policy. When the review is complete and a decision is made, a notice will be sent out to announce that decision."
Orignal SenecaDistrict.org post:
What remains unchanged for both sets of requirements is that a Palm is awarded for every five (5) merit badges earned beyond the 21 merit badges needed for Eagle or the last Palm. As before, this means a Bronze Palm for five (5), a Gold Palm for ten (10), a Silver Palm for fifteen (15), and appropriate combinations of Palms for higher totals.
The only change that applies to both sets of requirements is the elimination of a board of review. Since a Palm is not a rank, it was decided by National Council that a board of review was no longer necessary.
The difference between the two sets of requirements is this: For merit badges earned before an Eagle Board of Review, there is only one (1) requirement. For merit badges earned after an Eagle Board of Review, there are five (5) requirements.
For merit badges earned before an Eagle Board of Review, you count up them up, figure out how many sets of five (5) there are beyond the 21 merit badges needed for Eagle, and award the appropriate Palms to the Scout at his Eagle Court of Honor. That's it. Nothing else needs to be done. If there are any merit badges left over, they count towards the next Palm.
For merit badges earned after an Eagle Board of Review, three requirements are the same as before: Req. 2 - Demonstrate Scout Spirit; Req. 4 - Earn five additional merit badges; and Req. 5 - Participate in a Unit Leader conference.
The two remaining requirements have been updated: Req. 1 - Be active in the Boy Scouts of America for at least three (3) months; and Req. 3 - Set a satisfactory example of accepting responsibility or demonstrating leadership ability.
Req. 1 still includes three months of activity, but a Scout is no longer limited to activity in his unit. Activity in any BSA program is acceptable, including Order of the Arrow, Venturing, camp staff, NYLT staff, NAYLE staff, etc.
Req. 3 now permits "accepting responsibility" in addition to "demonstrating leadership ability." The reasoning here is that a Scout may earn Eagle by serving only in positions of responsibility, leadership being required only when a Scout is carrying out his Eagle service project.
IMPORTANT: The new requirements are not retroactive. If a Scout passed his Eagle Board of Review before 1 August 2017, he can earn Palms only by waiting three months for every five (5) merit badges earned beyond the 21 needed for Eagle. The new requirements for earning Palms after an Eagle Board of Review apply to these Eagle Scouts.
The official publication of the new Palm requirements is forthcoming. For details on the changes, open the "Boy Scouts" page by using this link and follow the "Eagle Scout" link. These details are based on the 10 July 2017 blog post, "The way Scouts earn Eagle Palms has changed in a big way," on Bryan on Scouting. This post includes additional explanations and comparisons of the new and old requirements which you may find helpful.
UPDATE: You can download the PDF which is National Council's official publication of the new Eagle Palm requirements using this link.