There is no "4GB wall" on ARMv7, as many ARMv7 cores support LPAE (Large Physical Address Extension), which is a concept symilar to PAE on x86, except LPAE uses 40-bit addressing. Meaning, that LPAE equipped ARMv7 can address up to 1TB of RAM.
It's also important to mention that upcoming ARMv8 cores, including A7, will not use 64-bit physical addressing. Most likely A7 will use either 40-bit or 44-bit physical addressing. Later giving access to at most 16TB RAM.
Of course either with LPAE on ARMv7 or in AArch32 mode on ARMv8, applications are still 32-bit, so the application itself can only access 4GB at a time. But I don't think it would be an issue on mobile devices any time soon.
You worry that apps will use more memory (64-bit pointers), but that won't be the case it the apps run in 32-bit mode (AArch32).
On the other hand ARMv8 provides other architectural improvements over ARMv7, which are not related to AArch64.
TL,DR: 64-bitness of A7 is marketing gimmick. Even on systems with more than 4GB RAM it provides no significant advantage over LPAE for 32-bit apps. And 64-bit apps aren't coming anytime soon.
Update: It's been confirmed by Qualcomm marketing executive (currently former executive, as he was demoted for these comments).
"I know there's a lot of noise because Apple did [64-bit] on their
A7," said Anand Chandrasekher, senior vice president and chief
marketing officer at Qualcomm, in an interview. "I think they are
doing a marketing gimmick. There's zero benefit a consumer gets from
A benefit of 64-bit is more memory addressability, but that is not
relevant in today's smartphones or tablets, Chandrasekher said. The
iPhone 5s has only 1GB of DRAM.
"Predominantly... you need it for memory addressability beyond 4GB.
That's it. You don't really need it for performance, and the kinds of
applications that 64-bit get used in mostly are large, server-class
applications," said Chandrasekher, who previously ran Intel's mobile
platforms group. (source)