I am here for this issue, as well. Perhaps I can explain it in another way, so that the importance can be better measured.
I use multi-inventory because I buy a lot of products from more than one supplier.
Every supplier has their own ordering policies and minimums and frequency of order.
When it is time to make an order from Supplier A, I use Stock Central to filter my inventory by Supplier A.
This used to show me a total inventory count (combined from all inventories), and a count of items purchased from Supplier A. It no longer shows this. This is bad.
Your two suggestions, using Out of Stock or Low Stock Threshhold, are both counter to our normal ordering process. We pretty much never want to place orders this way. We are, at any given moment, out of stock on maybe a dozen items from a dozen suppliers. We would never want to create a dozen POs for one item from a dozen suppliers, because all suppliers have minimums, and we build orders on a per supplier basis not on a per stock status basis.
I need to see, at a glance, while building a PO, what I have on hand, in total, across all inventories, for each specific item. That's how orders are created.
Imagine making a grocery list, opening up your refrigerator, and only being able to see what is at the very front of your shelves, and none of the products behind them. This is critical information to the decision-making process of building an order.