That isn't a trick you can use ad infinitum. There is a ceiling. It only really works if he pays for the lot and/or the resultant increase in value of the club then reflects or balances that outlay or at least sets up a position where it can in the future.
If he's not paying for the lot and loans are required, then there will be interest to pay that cannot be paid off by equity, unless he is able to sell at that increased value or be prepared to take that loss or is able pass on that debt to any new owners. Ultimately, the loss or debt has to land somewhere if that value increase is not achieved.
The MSP deal (if it ever completes) may potentially see him hand over 25% of the club's total shares for less than a quarter of the value of the stadium project alone (if his £760m cost is genuine). That may indicate the gap between speculation and reality and/or his desperation to get someone else to finish the job, to help cut his losses and perhaps sweeten any future sale.
The original financial plan never got off the ground. For most clubs that probably would've been the end of the project. However, given his wealth (and that of his backer) he was able to proceed. He was always going to fund the initial phase, so he pressed ahead regardless, in the hope that additional finances could be secured once the project was started and financial institutions would have greater confidence etc.... this never happened. So he then funded the subsequent phases....again, basically because he could. In for a penny, in for a pound (or 1 billion even). The recent events have shown that it isn't a bottomless pit and at some point debts or their consequences have to be met.
USM were always the ones who were going to fill those gaps..... with grossly inflated sponsorship deals if necessary. That safety net no longer exists.
The hope was that the stadium provided the step-change in everything needed to project the club to that next level. The hope now might be that it doesn't land the club with unsustainable debts or at least helps to facilitate a sale to someone who can absorb those debts.