Tier 4 is an unrealistic approach to the problem. As pointed out, the CUT is more often an occasional use tool.
As an example, not quite 100% accurate but- A base model B3200 will have an almost 20 percent cost increase in price because of this.
So, when are the credits, assistance, subsidies coming through for this? By and large, people don't buy a tractor purely as a recreational device or "toy" (well mostly.....). Yet, The government sponsored "cash for clunkers" to subsidize and increase car sales. Which, IMHO allowed those who could afford to upgrade- the opportunity to do so and didn't do anything for the majority of the country let alone the environment.
The tractor industry will suffer from decreased sales, lower need for production and ultimately layoffs and closing of plants...never mind the number of dealerships that may fold up. When all this happens- will the government step in to bail them out and pump money into this just as they did the auto industry?
If this is such an important step to protect the environment, then it should be affordable and accessible to all. If there is such a demonstrable need to get polluting engines out of service, why are there ANY exemptions?
...I now turn the soapbox over to the next candidate-