There's no way to expand the address space without breaking compatibility. A router is expecting IPv4 addresses, not 10.15.100.252.xxx.yyy addresses. All routers, firewalls, operating systems, programs, smartphones, etc would have to be replaced to support "IPv4 with 56-bit addresses."

Hexadecimal is shorter than the equivalent decimal representation. An 128-bit address would be 10.15.100.252.111.222.333.444.555.666.777.888.999.000.111.222. Use DNS!