I wish I could put a label like this on all of my products and I've been wishing for this for over twenty years, but the reality on the ground is that our support ends when the support for the individual parts in our product ends. We've looked at our supply chain periodically to see if we can replace parts with better documented/supported comparable parts, but frequently there just really aren't any better options.
This is a great idea in concept, but I fear that the flaw in the FCC's proposed rulemaking is that only indirectly addresses the root cause (the software, documentation, and support/updates provided by chipmakers for their parts). Furthermore, by focusing on device manufacturers who are the weaker partners in the chain, the regulation is likely to punish smaller, more innovative manufacturers.
If there are no buyers then their attitude should change.
Since the specific "IoT device for the USA market" set of buyers is actually a small percentage of sales for most of the parts they sell, they really don't care to support their product from the IoT security perspective. This support is expensive, so it would very likely be cheaper for them to ignore the market completely.
Most of IoT is that way. We had sales cycles that were 2-3 years long and they would in the end buy 300 units. I then go back to my suppliers and say 'hey support these 500 ic's that you sold me for 10 years from right now' They would laugh me out of the room unless I am showing up with big bags of cash. That instantly makes the whole project unviable to sell/support.