Hi Shava!
There are a few items to consider in this scenario:
1) Given that this is a government grant, they must identify you or the project as a subrecipient and explain why you or another entity are chosen, not anyone else. The sub-award management expectations will be the fiscal sponsor's responsibility, including managing and overseeing you and the project.
2) The other aspect to consider is budget. In either of these scenarios, the budget will have only two lines (sub-award and indirect costs). The fiscal sponsor will ask the sub-awardee to create the budget under which it will report. The official government budget will have only two lines as the other fiscal sponsor will receive and re-grant funds. And yes, I have not seen too many government-funded grants that expect and allow all of the funds to be subcontracted to another entity except for the indirect costs. Still, if the funder wants to fund this opportunity, they might. I would look into any limitations in the funding opportunity regarding the amount of re-granting you intend to initiate using this approach. Another approach would be to work with the fiscal sponsor and ask them to directly manage certain large parts of the costs to mitigate the appearance of all costs being re-granted.
3) Indirect costs. I suggest looking into this further, but from the guidance I have seen, the fiscal sponsor without negotiated NICRA will only be able to recover up to 15% on the first 50K of your sub-award. Then, your FS rate would apply to the funds that are re-granted. One must consider the overall G&A costs vs. the overall opportunity and commitment to work.
4) Option A implies the project is building entirely new infrastructure (if they are a model A project with you now). Please consider the additional cost that it might take to manage federal funds, and they will need to establish themselves with the government authorities and what is the long-term use of it. See if that still fits within the indirect costs, as they will probably not have the NICRA rate either.
5) Your current agreement. I want to ensure that, whatever you choose, you also amend the current agreement to document this particular exception.
Those would be the areas that I would look into! I hope this is helpful! And please do not hesitate to reach out to me with further questions.
BTW: One of the federal guidance on the sub-award management is below:
https://www.ojp.gov/tfsc/subrecipient_monitoring_guide_sheet_508