Precise measurements of the metastable helium (1s)(2s)${}^3{S}_1$ ionization energy have revealed a 9$\sigma$ discrepancy with QED theory that persists in isotopic measurements, suggesting a leptophilic bosonic interaction as a possible explanation. A subsequent investigation has concluded that only a scalar boson interaction would be consistent with the He observations. . Across the viable mediator-mass range of 0-800 eV, the He anomaly interpreted in this way implies a positronium $1{}^3$S${}_1\to 2{}^3$S${}_1$ shift ranging from (0.250)–(0.850) MHz, and a $2{}^3$S${}_1$ ionization shift of (0.140)–(0.210)~MHz. We discuss the feasibility of observing these shifts experimentally.