In AlphaWallet we briefly discussed the credit token in the week between 12 and 18th, but we didn't have the time to look into this or implement it by then. Here I list the arguments for it.
First, that AAVE made actions specifically for this token: delegate. (Delegate the line of credit (that is created as a result of depositing tokens and get aTokens) to someone else, with a few use-cases. Twitter post. If we don't have a token representation of it, we don't have a place to anchor actions related to this token (like Borrow and Delegate). Furthermore, the receiving user (who receives the deligation of the line of credit) has to borrow DAI, ETH etc. from that credit token, since she has no aETH., aDAI to start with (that's the reason why she wants to receive delegation in the first place).
Second, that currently credit information (or "Borrowing Capacity" or "Size of collateralised asset and collateralisation position" in plain English) is shared between tokens. For a user who has aDAI and aETH, it appears under aDAI and aETH, which misinforms the users that they are properties of aDAI and aETH, respectively, where it's actually a property of the collective collateralisation portfolio made up of both aDAI and aETH.
Third, currently, the borrowing process starts at the aTokens with a counter-intuitive flow. Let's say a user has aETH, and she wants to borrow DAI. She currently starts the flow from aETH token, but this action isn't really about aETH, and having "Borrow" action under aETH looks like, intuitively, borrowing ETH, where in reality ETH is the least likely asset she wants to borrow (since she may as well withdraw ETH - the fact she has aETH means she had excessive ETH in the first place and wanted something else).