Hello, unsprung mass.
Secondary suspension is critical to reduce track wear. Concentrating all the mass in the bogie would probably be a problem.
You also probably want bogie commonality between bi-mode and electric trains (thinking Class 800 sort of situation) because they're easy assemblies to keep spares of. In that case running a few cables (even thick ones for traction current) to the bogies is not such a big deal.
Another concern: Packaging. You still need to get heat out of the engine and you still need to have a not insignificant quantity of electrical control modules. You need a place to put your air compressor.
Also engines and bogies need servicing at vastly different intervals. Do you want to have to crawl around an engine every time you change a brake pad or wheel bearing? No sir.
That is why I said it would be very unlikely to happen. Will a 120-kW diesel-powered bogie be lighter or heavier than an equivalent electro-powered one? Can it be made as sturdy and reliable as needed? And, of course, can it compete on value?