The financial model for BMD has always been a bit sketchy. Initially it was heavily underpinned by the commonwealth games bid, which would've generated a lot of extra government funding. When that was brought forward by the collapse of the Durban games our bid's timeline was probably too tight, and Brum won it. There was then quite a long delay with more consultations, before the club announced the revised plans with a reduced 53k stadium. The finances were still sketchy but most turned a blind eye because USM had paid £30m just for first dibs on naming rights.... so there appeared to be no real concerns about paying for the build, and meeting any loan repayments going forward.
Of course, since then USM has been sanctioned (how permanently we don't know). On top of that Moshiri stated to the shareholders association in the summer that the costs had risen to £700-750m. We haven't been able to finalise any loan deal and we're still entirely reliant on bank of daddy.
I don't remember reading any real projections explaining how the costs were going to be covered, and have certainly not seen any that take account of the loss of USM and this construction cost hike (if real). I don't really believe increased capacity and new corporate will meet that shortfall alone. West Ham nearly doubled their capacity, yet their matchday income went down before increasing slightly. A lot will depend on how many wealthy blues and local companies are out there and the size of that latent support we want to tap. We won't be able to stack'em high and sell'em cheap to fill the place like West Ham.
As regards a comparison with redeveloping Goodison. Thats a false premise that was peddled by the club years ago, and long since disproven. Many of the larger clubs have shown that redevelopment is almost always the far cheaper option. Yes, it can be problematic in terms of acquiring more space etc, but generally adding 15-20k net new seats to an existing stadium will always be much cheaper than building 53k afresh. Let's face it, it cost £100m+ just to prep BMD. Liverpool created a stand as big as those at Wembley for less than that. Overall they will get to just under 62k for less than £200m construction costs. (Would've been less than £150m if they'd done both at the same time). That's a long way off the cost of BMD. Yes, naming rights might have been less attractive, but if USM was prepared to spend so much just for the right to be first choice, or to sponsor training grounds, then this certainly wasn't going to be an issue.
At present it looks like the whole thing is an exercise in packaging the club for a sale. Where that ultimate debt lands and how it is financed is anyone's guess.