Re: Solution for what?
The entire point of the proposal is to _force_ private interests to invest, recognising that they won't do so voluntarily. The problem is that neither public nor private institutions are prepared to invest in truly long term projects today and he's arguing we need to change the rules so that these investments are viable. One option, for example, would be to require investors to invest $1 in long term projects for every $10 they invest in anything else. Such things are possible through government regulation and proper oversight. Any such effort would have to be international of course.
Many of the economic institutions of today, such as a central bank and income tax, are quite recent inventions. Just because it hasn't happened before doesn't mean we can't do it, and people born in 50 years time may be surprised to discovered it was ever otherwise.
What we would need would be widespread buy-in that it is necessary. That's what we don't yet have. Hence, I presume, why this idea has been publically proposed now.