How much, on average, can a foreshortened nose be reasonably lengthened?

This is a common problem after primary rhinoplasty and usually results from the over resection of dorsal structures and residual lack of support... lengthening requires restoration of dorsal support usually through the use of long spreader grafts/septal extension grafts and tip support.... rib is usually the best source although sometimes septal cartilage will suffice.... the only real limiting factor is the quality of soft tissue/skin envelope and is rarely a ‘deal breaker’Find a rhinoplasty revision surgeon who has many years of experience/judgment, a practice focused on rhinoplasty and a penchant for revisions... membership in the Rhinoplasty Society is a good start

Lengthening a foreshortened nose can certainly be done.  Depending on your particular case, if a significant amount of lengthening is necessary, rib cartilage grafts may be necessary to provide adequate material to lengthen and stabilize the nose.  As mentioned in another colleagues answer, the limiting factor to lengthening the nose will be the skin and soft tissue envelope.  This can sometimes be a limiting factor in ethnic noses that need significant lengthening, but based on your description it is unlikely that your skin would be a limiting factor in lengthening your nose.  Of course, this would be best determined by an in-person evaluation.  I think it is very reasonable for you to achieve adequate length and projection.  It will be very important to select a surgeon who does a lot of revision rhinoplasty, as these tend to be more complex.