... points earned with your [credit] card were commingled with points earned with your [charge] card and all were redeemable under the terms of the full Membership Rewards program. I do not think this has changed, but have not seen any explicit confirmation. I will inquire.
No change. You will continue to be enrolled in Membership Rewards and accrue points on all eligible purchases. The communication recently sent does not apply to you, since you have your Nest Card linked to your Rewards Plus Gold Card. If you were to just have the Nest Card you would then be enrolled in the fee free Membership Rewards Express program.
I take this opportunity to remind that if you do not have a Nest (or Knot) credit card linked to your USA-issued Green, Gold or Platinum charge card you are missing an effortless 10,000 bonus Membership Rewards points each calendar year.