Starting a Payment Processor might seem easy from the start especially from the programming point of view but there's a lot more involved after the programming is over. Some people might ask "WHY" would someone want to start a Payment Processor when we already have PayPal? PayPal isn't accepted in some regions, some prepaid debit cards aren't working on PayPal and people need a little more flexibility and more of customer support with current payment processors. Integrating social media into a new Payment Processor might make it easier to gain popularity. Is it possible to get investors to invest in this kind of a projects with if the programming part is already completed?
It's not impossible to to, but it would be A LOT of work... A LOT... and probably not the exciting, interesting type of work, at least, in my eyes. Do lots of R&D...
It all depends on what is your target market. Starting a payment solutions is very easy. Thinking of promoters is just like analyzing your targeted market. The focus of the market will greatly determine its success.
It would need a Lot of Investment , You need to follow rules of Banks and Countries as banking rules are different all over the world . Mastercard,visa ,American Express follow rules of the bank . Customer support , team for Fraud and sales ,Marketing etc so its a lot of work .
I personally believe it is not worth on creating your own payment processor because there are so many of them already that you will spend millions advertising your own to get at least 0.001% of the world clients
The thing is some people are a bit disillusioned with paypal, you would have a chance to succeed if you did all your reasearch before diving in and had a good team of workers behind you. You would have to work really hard to make it a success. Remember there was also a point when no one knew what the heck paypal was.
Probably most chances to succeed would be doing some payment processor for countries, or people who can not use paypal or 2checkout.