Do you really like, or maybe even miss your old Spartan from either MCC, or Halo 5? I do.
How about an import feature is added which will create a perfect copy of your Spartan from your chosen game.
There are programs already out there that can pull models like this. Off the top of my head “Ninja Ripper” comes to mind. With some modifications it could rip the model, and be ready for use. Point being the ground work is already partially done here; potentially easy money.
Each import would cost maybe 25$ - 30$ per a single import. Given the technical nature of how this would be done it will be unlikely that imported Spartans could be customized after transfer which would render them to acting as the armor kits we have now.