What are the implications of Visual Descent Angle Not Authorized (VDA NA)?
This NOTAM is a Flight Data Center (FDC) NOTAM which is used to amend published Instrument Approach Procedures (IAP).  That means this NOTAM is effectively amending the procedure as the FAA hasn't had the opportunity to change the procedure yet.  This is probably due to a new obstruction that has been placed in the decent path.  Perhaps a new cell phone tower has been erected.  That is why it is always a good idea to check NOTAMs especially when flying under IFR.

EDIT:  To clarify a comment I made to OP, the MDA usually requires 350 feet obstacle clearance along the final approach segment.  However, when flying a glide path, the Required Obstacle Clearance (ROC) increases the farther away you are from the threshold (see graphic from Code 7700 Website).

The ROC is based off of the Obstacle Clearance Surface calculated for the approach.  Notice that if a new obstacle is erected somewhere along the glide path it is possible for the MDA to still be satisfied but the glide path ROC may have to change.  That is probably why the MDA is not changed in this NOTAM but the glide slope is Not Authorized.  

Quote from 7700 website:


  (1) If the OCS is penetrated, the OCS slope may be adjusted upward, thereby increasing the glide path angle. The glide path angle would increase because it is dependent on the required slope.