I've been waiting for NVDIMMs for 30-some years it seems, since I used to run an Atari ST with 4MB battery-backed RAM cartridge.
Instant-on isn't really an issue (though we pretty much had that, back in the ST/TT days) - today it's just about the OS page cache. PCIe SSDs still aren't as fast as the real memory bus, and the fewer times we have to make our data traverse that the better. For databases you always want fast writes, and the fastest write is the one you didn't need to execute (e.g., because it was in cache, and the block got overwritten by a subsequent update anyway). NVRAM inside disk controllers is still at the far end of the I/O bus from the CPU.
NVDIMMs offer the perfect solution - cache everything, don't ever worry about flushing data back to secondary storage unless the cache is actually full. If there's a power failure, after reboot just keep on going with the cache exactly as you last left it. The trick of course is that you need explicit BIOS support. At the very least, to make sure the POST memory test doesn't zero out all of your precious NVDIMMs just as they're reloading themselves with power being restored. And you also need explicit OS/kernel support, to use the cache structures as they already exist, instead of (again) just blindly initializing to zero on a reboot.
Whether NVDIMMs ever offer you instant-on is irrelevant. The real value, and the reason why you want these in servers, is perpetual high speed cache to mask whatever slowness of your HDDs or SSDs.
... and on the note of databases and RAM, this is what I've been working on these days http://symas.com/mdb/inmem/
It's a big deal for all the tech giants - Google, Facebook, Twitter, eBay, you name it. NVDIMMs can be salvation for them (with the correct database technology, of course) and a gold mine for the vendors who bring them to market first.