Excellent question! This is what BLD staker governance is all about. As it says in the Inter whitepaper:
Governance determines the approved collateral types
That decision hasn’t been delegated to anything smaller than the whole BLD staker voting process. So to question 5, no, the econ committee can’t add a new collateral type.
So a proposal to bring on axlETH or the like as a Vaults collateral involves discussing such risks to the satisfaction of the BLD stakers.
Recall also from the Inter whitepaper:
2.5 Multiple levels of protection
The Inter Protocol implements several levels of economic protection to ensure that IST remains
100 percent backed, even in the case of a large drop in the price of collateral:
Overcollateralization and Liquidation
Reserve pool and IST fees
BLD issuance
By way of precedent, recall the proposal to add PSM contracts for DAI_axl and DAI_grv:
The Economic Committee also has an important role to play: once the decision to approve a collateral type is made, the EC controls parameters noted above: Mint Limit, Collateralization Ratio, etc. These parameters can be used to mitigate bridge risk.
Again, by way of precedent, recall the discussion of starting small and expanding those limits for the PSM launch: