[RFC] Remove SetFeesMode instruction

proposals/0000-remove-set-fees-mode.md

@@ -0,0 +1,48 @@
+---
+Title: Remove SetFeesMode instruction
+Number: 0
+Status: Draft
+Version: 5
+Authors:
+ - Francisco Aguirre
+Created: 2024-05-23
+Impact: Medium
+Requires:
+Replaces:
+---
+
+## Summary
+
+The `SetFeesMode` instruction and the `fees_mode` register allow for the existence of JIT withdrawal.
+This mode complicates the fee mechanism and leads to bugs.
+The proposal is to remove said functionality.
+This RFC doesn't require RFC#58 but it works alongside it to simplify fee handling.
+
+## Motivation
+
+The JIT withdrawal mechanism creates bugs such as not being able to get fees when all assets are put into holding and none left in the origin location.
+This is a confusing behavior, since there are funds for fees, just not where the XCVM wants them.
+The XCVM should have only one entrypoint to fee payment, the holding register.
+That way there is also less surface for bugs.
+
+## Specification
+
+The `SetFeesMode` instruction will be removed, meaning its corresponding paragraph on the spec will also be removed.
+The `Fees Mode` register is not listed in the XCVM Registers list on the spec, so that'll be unaffected.
+
+## Security considerations
+
+The proposal aims to improve security by simplifying and reducing bug and attack surface.
+
+## Impact
+
+The impact will be bigger than that of introducing a new instruction, but it will still not be high as it will go in a new XCM version.
+XCMs before this RFC that use the removed instruction might work in unexpected ways if the XCM is converted to the new version.
+
+## Alternatives
+
+None.
+
+## Questions and open discussions (optional)
+
+Was this feature adding any value to warrant the added complexity?