I like the idea of your broadhead adapter. My first impression is that they will indeed be stronger than a typical threaded adapter but as you pointed out only testing will prove or disprove their strength.
As for myself... I use a 100 gr brass insert, plus a 125 gr threaded adapter, and then add a 225 gr broadhead to my arrow. So for those of us who are building for extreme, and ultra-extreme, FOC may I make a suggestion? It would be beneficial to incorporate an "add a weight" type system into your adapter, something similar to what Gold Tip does with their brass inserts, which allows for adding 25 or 50 gr weights to the insert, allowing the user to add as much weight as is desired. This would cut down on cost of manufacturing and give the end user the ability to customize the adapter to the weight they desire. However, I do not know if they hold a patent on the design and system. (Just one mans opinion)
If testing proves a strength benefit vs threaded adapters, and if weights met my criteria, then I would gladly purchase and use the adapter.