5 months post op BBL, have cellulite, stretch marks and a dent. Is my BBL revision realistic? (photos)

Yes, this can be revised. Revision would consist of removal of excess fat, particularly the sides to get a more natural contour and fat transfer to the dent. SAFE lipo and Cellulaze would greatly improve the cellulite appearance of the buttocks.

    This will require much more skill than one may imagine to correct shape and excess at the same time without creating droop of the skin envelope.

Inside of six months, you still should be waiting as you still are not at final results, but I agree it is less likely these issues will resolve at this point.  The skin irregularities can be due to stretching of the tissues from the fat, though this isn't common, it happens once in a while.  There are non-invasive options for trying to improve the skin contour, and yes surgery is an option but the results tend to be mixed.  However, reducing the fullness on the sides is very achievable and filling in the dent on the right is also possible.  So a revision procedure - by an experienced BBL surgeon has a good chance of improving the overall situation for you.