Among them: The Pats proposed for the elimination of the red challenge flag, and instead suggested that challenges be initiated with a team calling timeout before the next snap.
Here's more of the Patriots' proposal, via the NFL's release:
"If a challenge is upheld, the timeout will be restored. A challenge will only be restored if a team is successful on both of its challenges, in which case it shall be awarded a third challenge, but a fourth challenge will not be permitted under any circumstances."
New England also has proposed that teams can challenge under the two-minute warning.