Here's the payoff on the U.S. side: under the program, if Japan grants a claim, an applicant can request that the USPTO "fast-track" the claim. How fast anything happens as a result is unclear; it's a pendency thing.

The program excludes all PCT applications, provisional applications, plant and design applications, reissue applications and reexaminations. If you just want your patents in the U.S. and Japan, this highway is for you. International applications: forget about it.

An applicant requests that an application be allowed on the highway. Applications that qualify under the program receive "make special" status (refer to 37 CFR §1.102), and are queued before measly U.S.-only applications that aren't special too.

To qualify for the U.S. version of the program, the corresponding Japanese application must have at least one granted claim, and U.S. examination must not have begun. If the Japan office requires the same, a foobar Catch-22 problem arises; but Japan's version is unknown at the time of writing, as the press releases were not, ahem, coordinated.

Certified translations must be provided, and the claim limitations must be essentially the same: "of the same or similar scope." The plan calls for using translation machines, which Japan has already introduced. Nothing makes for readability like a machine translation, or, as the machine translation would have it: "read same if machine translate like nothing". Have a claim like that stand up in court and see how it fares.

Claim amendments must be synchronized. If either agency decides that the claims don't correspond, the applicant will be found non-compliant. It's like an Alka Seltzer ad just waiting to happen.

The prior art is shared between the offices. This is the supposed economy to be derived from the program: shared prior art discovery hypothetically raising patent quality and expediting examination. Applicants must obey 37 CFR §1.56 (duty to disclose prior art).

The politics of two examiners who don't know each other, and can't communicate due to a language barrier, with no experience in this kind of thing, trusting each other enough to grant claims based on the other's say-so, is incalculable to the point of bizarre.

The program is subject to termination "if the volume of participation exceeds manageable level." Translation: too much pissing & moaning by examiners will put up a sign on this little thoroughfare: no thru traffic.