Doesn't Excalibur replace the original staff , so contains the gems on the gem screen anyway ?
i mean like a crafting system in game like if you get enough fire gems you could craft a fire staff for Chloe so she is not useless when you skip her turn same for akane maybe with an ice staff and a shield staff for Dylan!
upgrades to living sentient Armour so you can add shield gems into it and get a permanent shield
upgrade Excalibur with a rage gem so you get like 10% rage of the gem you put in there and it becomes inherent to you like the shield
ofc those upgrades would be prohibitively expensive like adding a level 8 shield gem would be 80.000 pounds upgrade and up to between 5 and 8 gems
as for the magic staffs for your chosen and companions besides the cost of the gems it should cost like 10.000 pounds, put it like a fee being paid to that master Armour smith the one that got you the shield removal bolt!
so very expensive but with small advantages!
- edited -
Almost forgot adding certain gems like above tier 8 into your Armour would give you immunization from things like fire lightning or ice