If this proposal goes into effect, by clobbering local zoning codes, anything with sufficient money behind it is going to get built. This typically means projects that optimize for the developer's ability to extract rent from residents: 3 or 4-story apartments with small unit sizes, basic finishes made to aesthetically look high-end, and bare minimum green space or community space. A common approach is to use high-end appliances, a one-time cost, to ask for higher rent. This is the sort of construction that pops up in American suburbia today, where there's sufficient demand, and gets adapted to a more "urban" form with flat roofs and minimal changes.
Despite many of these projects being built, there's a price floor beyond which the rent will not drop, because the developer has to make payments on loans and maintain a profit. Therefore, while housing affordability is sure to improve in some places where it's absurdly high, it won't meaningfully be altered in places whose urban form is predominantly suburban. This is doubly so because the plentiful supply of single-family homes offers an a low-cost way to get started as a landlord.
Developers also have a choice on where to build. If it's cheaper after expenses to assemble a large parcel in Morgan Hill or Tracy or Vacaville, build out the site, and charge those rents, than to do the same in West Portal, one of them isn't getting built.