Research directions in persistent homology

Persistent homology has applications in symplectic geometry. For one striking example, see the recent paper Autonomous Hamiltonian flows, Hofer's geometry and persistence modules by Polterovich and Shelukhin. They use persistent homology to give very explicit examples of area-preserving diffeomorphisms of closed surfaces which cannot be included into $1$-parameter subgroups of such.

Persistent homology is related to spectral sequences. There is already a discussion Persistence barcodes and spectral sequences about if this leads to new theoretical insides and there are stated further references (for example, there is stated the book of Edelsbrunner and Harer, which is a standard book for Persistent homology and can find further discussions about some research directions in Edelsbrunner and Harer's works as well).

Furthermore, Persistent homology leads to discrete Morse theory, what can be used for computing cellular sheaf cohomology (if you want to know more about it, i.e. Justin Curry's work could be interesting for you).