Does the new I-526 processing policy apply to cases filed in December 2018?

Yes. You may experience a faster processing. However, there is no expedite processing.

It may go faster as they switch off of the first in first out a policy to adjudicate cases in order of their priority date being current.

The new policy should speed up pending cases form all non-backlogged countries. Technically anyone can apply for an expedite but it must meet published expedite standards.

Since your country of chargeability (country of birth) is not China, India, or Vietnam, your I-526 petition stands a good chance at being adjudicated before other I-526 petitions filed by EB-5 investors from those countries whose priority dates are not current. USCIS-posted processing time for I-526 petitions, however, remains at 31 to 50.5 months. USCIS does have expedite criteria, but expedited requests are strictly scrutinized and very few are approved. The criteria are posted at: https://www.uscis.gov/forms/forms-information/how-make-expedite-request.

The new policy applies to all cases, so it is possible that your case will be reviewed before other cases that were filed before you by Chinese nationals.

Yes, under the new rule, the processing of your case should proceed faster than originally expected as there is no visa backlog for Egyptian nationals. Other options to expedite depend on your particular circumstances.

The new policy should apply to you as it relates to whether based on your country of birth you are not subject to visa backlogs.

The processing times apply to all applications whenever they were filed.