I would want to add my own ideas of interpretation and application too. I wrote to the original author and they responded, and I think they'd be ok with the project? I couldn't discern a clear answer from them yet.
To me this suggests that you plan to write an elaboration of a previous paper in collaboration with the authors of the previous paper.
As a reviewer I would have no objection to such a research plan: incremental research is perfectly fine, so please give the appropriate slant to your manuscript.
As a reviewer I would also feel obliged at a minimum to browse the literature you cite -- is it workable to add a link to the obscure source? I would then soon realize that your work is all the more valuable to the community.
The Vancouver recommendations, primarily intended for biomedical publications but easily to generalize to any field based on common sense, suggest that
authorship be based on the following 4 criteria:
- Substantial contributions to the conception or de-sign of the work; or the acquisition, analysis, or interpretation of data for the work; AND
- Drafting the work or revising it critically for important intellectual content; AND
- Final approval of the version to be published; AND
- Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
In addition to being accountable for the parts of the work he or she has done, an author should be able to identify which co-authors are responsible for specific other parts of the work. In addition, authors should have confidence in the integrity of the contributions of their co-authors.
All those designated as authors should meet all four criteria for authorship, and all who meet the four criteria should be identified as authors. Those who do not meet all four criteria should be acknowledged -- see Section II.A.3below. These authorship criteria are intended to reserve the status of authorship for those who deserve credit and can take responsibility for the work. The criteria are not in-tended for use as a means to disqualify colleagues from authorship who otherwise meet authorship criteria by denying them the opportunity to meet criterion #2 or 3.Therefore, all individuals who meet the first criterion should have the opportunity to participate in the review,drafting, and final approval of the manuscript.
So, if the potential coworkers are not clear-cut in the intention of co-authoring this work (that is, doing something), you may resort to simply citing their previous work.
A note of practical wisdom: if the obscurity in writing reflects obscurity in thinking rather than merely poor command of language, you should consider whether your effort will be mutually collaborative.
It would be unethical on their part doing nothing and exploit your good intentions.
In the perspective of an editor/reviewer I am interested that there are no ghost/ guest/gift authors -- please have a look at this decision chart of Publicationethics.org and its references.
Last but not least: ask for an opinion to the editor of a/the journal you intend to publish in. You may do it at two different times: before getting started, speculatively; when you approach the near-final state, for you might find other interesting corollaries along the ways. In the second case, I imagine, you will afford being more assertive about the cutting edge in your manuscript.
Good research hinges around merit and credit. From your words I feel you are doing well.