What will it take for Google to bring 64-bit support to Android?

The same major roadblock as always

All of that aside, you hit the only real roadblock, which is the same roadblock that has caused problems with Android since its first days. Google would have to do something that it has never been able to do before with Android - getting developers and manufacturers to follow the plan, not jump the gun on hardware, and push software updates quickly.

This has been a constant struggle for Android, and one that has been getting better over time, but one that still isn't fixed enough to make the transition to 64-bit any easier. As we’ve seen with tablets and multi-core processors, Android hardware makers never want to wait for the system to be optimized before introducing new hardware. Android tablets first shipped well before the system was ready, leading to the forgotten Android 3.0 Honeycomb update, which was just a stop-gap on the way to the proper Android 4.0 Ice Cream Sandwich update. 

The real work will be in getting developers to update apps with native code for the new 64-bit platform; but it is obvious that the 64-bit hardware is coming soon, much sooner than it will take Google to update Android for 64-bit. This will lead the whole ecosystem to end up in the same vicious cycle where manufacturers will push hardware before the software is ready, and then will likely be slow to update software once the optimizations are done. The first part of the problem will likely occur not through any fault of Google's, but rather because manufacturers (read: Samsung) will want to make sure they have that 64-bit processor in the newest flagship device - and more importantly, in its marketing campaign - before Android is ready to handle it. Then, once Android does get the update to 64-bit, users will have to wait a bit for manufacturers to push out that update.

Of course, this isn’t necessarily a problem for consumers per se, more of an annoyance for those of us who pay attention and understand the real story. All it means is that we will all be subjected to marketing campaigns touting features that offer no real value, which is nothing new. We've seen plenty of features gracing various marketing campaigns that don't really make much difference to the majority of users, like Air Gestures, Face Unlock, and Siri. Samsung and others will undoubtedly market that their products have 64-bit processors, and will conveniently leave out that they offer little to no benefit because the software isn’t ready. But, that is the way marketing works all around anyway, and the average consumer won’t know the difference anyway.

A slow path to faster speeds

While hardware manufacturers plan to jump the gun and put out 64-bit hardware running software that isn’t optimized, Google hasn’t mentioned at all when we should expect a 64-bit optimized version of Android. Getting there will doesn’t look to be that rough of a road, but it will certainly take time to get there. So, it’s impossible to say when Android will be fully optimized from top to bottom.

The earliest we could hope to see Android with proper 64-bit support and optimization throughout the system would be in the summer along with the Nexus 7 (2014), but even that is pushing it too much. More likely, we’ll see a minor update to Android 4.4 KitKat at Google I/O, and Android 5.0 (Laffy Taffy, maybe?) with proper 64-bit optimization in the fall with the Nexus 5 (2014). Even then, users will have to wait for manufacturers to update devices; and, to make things worse, that hardware is likely going to be claiming 64-bit on spec sheets well before Android is ready.

All of this needs to be sorted out, because ARM processors are quickly hitting a performance plateau, because of an outdated instruction set architecture (ISA). ARMv8 has introduced a completely new ISA, and made the switch to 64-bit, both changes which will lead to faster speeds as long as software is optimized properly. Unlike on desktops, the argument about hitting the 4GB RAM limit is nowhere near the most important factor when talking about the performance benefits of moving to ARMv8 and 64-bit. Clock speeds can’t get much faster without causing heat and battery issues, and adding more cores will only get you so far, unless they are specialized cores to offload low-power processes, like we’ve seen with the motion and voice coprocessors in the Moto X and iPhone 5s. The most efficient way to increase performance on an ARM chip is to switch to the ARMv8 architecture because it can do the same in a single transfer as 32-bit ARM can in as many as 32 transfers, but that requires the software optimizations before you see the real performance increase. 

So, we should all prepare ourselves for a lot of empty promises from Android hardware makers over the next year. But, if we keep an eye on Google, and the news coming out about the official software optimizations, we should get a much better idea of when to expect the real changes. 64-bit is certainly on the way, but the real news will be when Android is properly optimized for ARMv8. 

reference: Is Android 32-bit or 64-bit?, Android Developers 1 & 2, +Android Development Community (a special thanks to Bartlomiej Janusz for being so patient with my questions)