> Who is going to pay for companies to develop these vehicles?
VCs and other investors who see a company that wants to build these vehicles for cheaper launches? I don't really understand the point you are trying to make. Yes, it's expensive to build X, but usually $Y motivates people/companies to invest in the initial costs to cover building X because the payoff, $Y, will be greater than the cost. The news here is that the initial cost is potentially MUCH lower because now they can use this airplane as a stage 1 and not have to develop their own.
> VCs and other investors who see a company that wants to build these vehicles for cheaper launches?
So, a currently non-existant SpaceX 'competitor' that wants to hitch itself to the success or failure of Stratolaunch?
That's an incredibly sketchy business to build. You'll be sinking a billion or five dollars before you have any hope of seeing a cent of revenue, and then having an unknown probability of discovering that reusable rockets will eat your financial launch.
Right now, $X is measured in the billions, $Y is anywhere between 0 and billions, and there's a %Z chance (Which is probably over 50%) that your complement product (Stratolaunch) will die before you get a cent of revenue.
Developing and certifying a new rocket is an incredibly expensive affair. What are the cost savings this promises, compared to SpaceX?