Just using your initial list how does the blockchain help with M&A? The role of investment bankers in that aspect is to do research. Due diligence, pricing, etc (as well as specialized finance at times).

Or trading derivatives? Derivatives are either traded on extremely efficient exchanges already (the automation of which put a squeeze on IB profits) or are for very bespoke products. I suppose in this area you can come up with a process for making the bespoke products more efficient via the blockchain but the actual ledger on those things isn't the hard part, its the contracts and risk pricing. Even then, the banks customers seem likely to continue to go to them for the expertise in the bespoke products.

For underwriting securities its not clear how the blockchain makes transactions less risky? Again the mechanics of the ledger are fairly easy and efficient already. I suppose there is room for improvement, but the thing people are going to the IB for, and what generates their profits in this area is actually taking on the risk, which the blockchain does not mitigate.