I don't think this is the correct approach, it's not the size of the company that is the problem. In fact large companies (not monopolies) can produce/offer services/products that smaller companies can't due to the scale (i.e. mobile banking). What should happen is the employees or execs responsible should have gone to jail for life for the destruction they caused providing a deterrent effect, and also much stronger regulation policed by a truly independent regulator with the teeth to act.
In China people can be sent to jail for 'causing destruction' but in western countries you have to have been proven, beyond reasonable doubt, to have broken a law.
Most of the activities the banks were carrying out that contributed to the crash were well known long before the crash, and were not illegal and they weren't being called out for it. In fact many politicians and the public were keen for broader availability of cheap loans. So yes, we need better regulation of financial institutions, but there were many causes of the financial crisis and blame lies in many places and many lessons learned, but you can't apply laws retroactively or arbitrarily.
