Re: Two balloon
The four-balloon idea is neat, if they do consider a cluster balloon again. It could be made workable by adding about 10% more helium to the top balloon.
One big problem with the two-balloon approach is that the tension waves along the support lines will destabilize the platform. I think it’s a bad idea in any case to depend on a flexible line for moment resistance — never try to push a rope! Stabilizing gyros on the platform are important in any case.