Hi,
Living in Japan, I couldn’t register to the app because the region isn’t supported.
Are there any plans to support it in the future ? If yes, do you have a time frame ?
Otherwise, what are my options to use this service ? Can I register somebody else’s address in another country and use the app from Japan ?
Cordially
You have to be a legal resident of any EEA country right now. You won’t be able to verify your account. You can check the FAQs for more details. 
Well, technically, being of French nationality with a valid french passport, I could verify my account using my parents address in France… Just not sure about the nitty-gritty details regarding the residency laws.
Looking at the FAQ, I moreover see that Revolut can deliver the card via Express Delivery to Japan in 1~3 working days. This is confusing
Check the section „How to verify my Identity.“ If you would register with the address of your French passport, identity verification should be okay.
I recommend you talk to someone from Revolut directly, via Twitter or Facebook, for example. There are some hurdles to overcome. Or you can send someone from Revolut a direct message here as well.