Harold,
I agree with you in that HPT can be used "as an enabler to get to first base in instructional systems design (ISD)." Unfortunately, I believe there is a gap between HPT and ISD. HPT focuses on the front-end analysis and ISD focuses on instructional design. This is evident from Leigh & Traceys' (2010) article titled 'A Review and New Framework for Instructional Design Practice Variation Research' where they identified that "needs assessments are conducted infrequently" (p. 36) within the field of instructional design. I believe that ISD and HPT need to join forces to re-emphsize the importance of the analysis phase in ISD - the HPT component of ISD.
Thanks for the information you are posting. I have found it be insightful and informative.

References
Leigh, H. N. & Tracey, M. W. (2010). A review and new framework for instructional design practice variation research. Performance Improvement Quarterly, Vol. 23, No. 2, pp. 33-46.