"Private money or a partnership with a wealthier junior are the only options."

You appear to be correct. . . . .Unless someone out there is willing to say farewell to orthodoxy.  I really don't understand why everyone at a certain level or size in the industry is so Hidebound.  The lack of imagination and tolerance for even relative peanuts of risk has got to be killing future opportunities.  Fortune favors the bold and the times are always changing, but it appears to be a culture of fear-based "strategic" thinking - EXACTLY THE OPPOSITE OF WHAT MULTI-YEAR FORWARD PLANNING REQUIRES.