More advanced magnetic breadboard with software defined wires
Couple of my thoughts: 

The mass market for components is to be soldered to a PCB and this is what components are optimized for. That you can use these components on a breadboard is an advantage for the user, but the manufacturer has little to non interest in that. Therefore you would need special breadboard-compatible components. You don't want to pay a $1 for a diode that costs  $0.005 just because it has magnetic/breadboard properties, let alone that you don't want to have a double stock (breadboard vs. production).

Breadboards already have huge parasitic capacitance, inductance and resistance from their own, you don't want huge amounts of extra wiring to increase these properties even further.

FPGA's are expensive, a regular breadboard sells for a few dollars/euro's.

Components on breadboards regularly release the magic blue smoke because of misconfigurations. You don't want the FPGA, probably being the most expensive part on the breadboard, to release its smoke.

It is much easier to quickly fiddle with wires than to upload netlists while experimenting.