I can't imagine Japan can afford to continue its policy of outright lockdown well into 2022. All those billions of dollars invested in new hotels and infrastructure for an Olympics that never happened aren't going to repay themselves. My best guess is that not long after this upcoming disastrous attempt at an Olympics fails and passes, the government will have to very seriously reconsider its current policy on banning outsiders.
That said, regarding "vaccine passports," no idea what Europe and Asia are planning to do but I wouldn't count your chickens just yet with regards to America. Stateside, the governors of red states and Republicans in Congress are vowing to fight the very concept of vaccine passports, framing them as some sort of Orwellian, communist overreach by a leftist, dictatorial government bent on creating a new caste system in America. In other words, the MAGA hat anti-vaxxers are pissed off that the government is going to allow private airline corporations to require passengers to be vaccinated, thereby complicating their plans for a cheap-ticket pandemic vacation to visit their shit-kicking cousins in Florida so they can pack Daytona with 100k other drunken, screaming, maskless illiterates and make sure their entire clan of obese, diabetic inbred relatives all end up in the hospital.
One thing to consider, however, is not Japan's policies but the policies of the rest of the world. As always, Japanese and their government see themselves as the "clean" folks, and the rest of the world are the filthy vectors of this virus and need to be kept out during this pandemic. But seeing as how Americans are vaccinating over 3-million citizens per day, over 40% of the country has received at least one shot and a quarter of Americans are now fully vaccinated--while the entire nation of Japan can't even vaccinate enough people each day to fill a concert hall--we are very quickly approaching the point where the average citizen of Japan will be the most likely carrier of disease, and the citizens of every other civilized nation on earth may not want Japanese coming to visit them, pre-test or not.
Personally, I'd love to see the US/EU issue a blanket ban on all Japanese visitors over safety concerns. It'd probably work wonders in terms of forcing the Japanese government to get its shit together with vaccination efforts, and also a well-deserved slap in the face and wake-up call to the entire stunted population that thinks it's somehow less infected than the rest of the world. You roll out the red carpet for the curb-squatters of the Middle Kingdom and you get everything that comes along with all that tourism money.