I assume that it could work as a temporary solution but the article hints that this problem will likely become global soon. So, instead of moving numbers, it's easier to add some and increase the possible combinations.
15 digits can make for 1,000,000,000,000,000 different card numbers, leaving 16th digit for checksum. This is a completely made-up problem, caused by chopping the number into card type, bank id, etc.
I think it's better (for Japan) to force it into a global problem than a domestic problem. Then more people will care about fixing it and the issuers will retain international interoperability.