I think I have a different perspective;
To provide a good overview of all financial accounts is a totally different type of product - like moneyhub. For chip to try and do this as well as provide savings and investments would distract chip from its core focus.
However, surely that makes it more important for chip to provide an API, if we expect chip to become core to an individuals savings and investment accounts? The trend is a desire to get a single overview of your financial position, to make it simple and accessible. I’m really not clear therefore how chip can justify not offering it, or have I missed the point?