I have very few ideas on this, which are

• essential infrastructure should not be run for profit but for serviceability
  
• retail banking and the payment and clearing system are essential infrastructure
  
• money creation is being licensed for free by the monetary authority to private, for-profit entities, with various forms of implicit and explicit state backing of liabilities. This needs to end. Money should be created by being spent or lent directly into the economy, destroying any inflationary excess via taxation. Service provision by bank for this purpose is also essential infrastructure.
  
• securities are credit instruments. Primary securities issues are investment through credit. Investment banking in so far as it provides the credit to issue securities or fund project is also essential infrastructure. The secondary markets for securities are speculation, also known as gambling, and not essential infrastructure
  
• gamblers can continue to play at the casino of secondary securities markets, but we should not pay attention. It is the job of the regulatory supervisors to ensure that gamblers cannot bring down the essential banking infrastructure. Like all gambling, securities markets speculation is a sign of excess disposable wealth and income, and should be taxed heavily.

En un viejo país ineficiente, algo así como España entre dos guerras civiles, poseer una casa y poca hacienda y memoria ninguna. -- Gil de Biedma

I think all profit related transactions should be subject to a tax which is levied according to the time the investment lasts. Effectively what you're trying to do is encourage societally worthwhile practice and punish those which are parasitic. I appreciate that a hundred financiers could debate the definitions of those for some time and come up with no conclusive answer, but I'll go with Lord Turner for starters.

EG Buy shares and hold them for a year and a day = tax exempt. Trade them back and forth in a day = punitive.
Forex trades may require different timescales.

keep to the Fen Causeway