Grant HYM Investments generous tax credits/abatements to go slow on the Suffolk Downs redevelopment such that Suffolk Downs and this new land that was Logan could be studied and reimagined by experts with an eye toward making it a holistic redevelopment program that also included a long-term vision for Belle Isle Marsh--while keeping the latter a reservation.
Whether that means conveying the "new" Logan land to HYM, or bringing in another development partner to make them act as a kind of consortium, who knows.
After all, other than the Blue Line and Bennington Ave., Belle Isle Marsh is highly contiguous/interacting with Suffolk Downs' ecosystem. And on a straight line, the southern edge of Belle Isle Marsh is just 800 yards or so from the northern tip of Logan. Treating the three entities like a single unit could do a lot in terms of restoration.
Simply put, whatever HYM Investment would be permitted to do at Suffolk Downs in terms of balancing between urban development/ecological restoration, that should be eyed closely in terms of a similar scheme for the Logan lands--while not neglecting Belle Isle Marsh as the vital connector.