Softbank should not be allowed to invest more than ARM Holdings sold at a loss.
If I was an AI enthusiast, Softbank showing up would make me nervous.
If the Softbank's inversion is limited to their available assets, or the exposition of each lending is limited to a portion of their real reserves, I think such event will not happen (more than burned money by a bad inversion).
I think it would be quite similar to what has already happened on a global scale with the public money of each country in 2008 (due to the banking pyramid scam), or since 2011 with public loans to TEPCO, an event that could have been prevented if the central plant had been built were originally planned.