Geant4 Does Not Invest in Long Term Performance Improvement
The Geant4 team (collaboration) does not invest in long term performance improvements required to be able to afford simulations requirements.
Amount of simulation required may not be affordable or achievable with anticipated resources. Physics analysis and quality would suffer; or some physics channels may be delayed.
Invest in a major R&D program to devise strategies for fast MC, as well as better use of compute architectures. This requires a complete re-engineering of the Geant4 software to be able to achieve significant performance improvements (factors 5-10) on modern CPU architectures. In addition strategies for fast simulation are required, as well as associated physics validation work.
This is a long term strategy that must be invested in. Some R&D work happened in the context of Geant V, but an appropriately scaled set of R&D work is not yet visible.