With Google's (NASDAQ:GOOG) (NASDAQ:GOOGL) main keynote at its annual Google I/O developer conference out of the way, it seems that the company's Nexus line of devices -- namely the Nexus 7 tablet and the Nexus 5 phone -- have yet to receive replacements. However, investors shouldn't necessarily take this to mean that such devices won't be incoming. Indeed, these products' successors may very well launch in the fall along with Google's new Android-L operating system.

Not all Android devices are created equal
If you're a developer for Apple's platforms, getting a real device to test on is easy -- just buy a reasonably modern iPad or iPhone and you'll be able to use all of the latest and greatest operating-system features, since Apple very diligently updates several generations of iOS devices to the latest edition of iOS.

With Google's Android, things are a bit different. Most handset and tablet vendors that use Android are responsible for making sure that their devices get updated. Many Android vendors -- whether it's due to resource constraints or simply a desire to place an incentive on device upgrades -- tend to be very slow in updating older devices to the latest version of Android.

So how can developers make sure they have hardware readily available to test their apps on the latest version of Android?

The Nexus program is still vital
Google offers what are essentially glorified reference platforms with its Nexus line of devices. While Google had once offered a Nexus phone, and a small and large pair of Nexus tablets in the Nexus 7 and the Nexus 10, it seems that the search giant has whittled that down to just the phone and a small tablet.

These platforms run "stock" Android -- that is, Android without any of the skins and other software that many of the other vendors such as Samsung, Asus, and others tend to include. More importantly, these devices get the latest version of Android before any other devices do, making them perfect for developers.

Will we see new Nexus devices this fall?
While Google didn't introduce any new devices at Google I/O, it makes perfect sense that no new devices were released. The newest version of Android-L won't roll out officially until the fall (although developers will soon be able to download a preview of it for their Nexus devices). It makes sense, then, to not roll out new devices until the new OS is buffed, polished, and ready to go.

Waiting on 64-bit silicon
Further, it's very likely that Google will want to ship devices running 64-bit processors to really "show off" this support in the new OS. Since Qualcomm (NASDAQ:QCOM) is likely to have 64-bit low-end processors available in devices during the Q3 timeframe, it wouldn't be surprising to see a fairly inexpensive Nexus phone with a Snapdragon 410 or 610 (both sport ARM Holdings' Cortex A53 chips) to hit the market around then.

On the tablet side of things, Google could direct its hardware partner to use the same Cortex A53-based processors from Qualcomm. If this is a low-cost device, Snapdragon 610 from Qualcomm would make sense, as this is the successor to the Snapdragon 600. (Technically it's a hybrid Snapdragon 600 and Snapdragon S4 Pro, but this detail isn't important.)

That said, if Google wants to go high end, its best bet is probably to go with the Tegra K1 64-bit from NVIDIA (NASDAQ:NVDA), which NVIDIA claims will be available during late 2014. This chip should offer pretty phenomenal single-threaded CPU performance as well as class-leading graphics performance. In fact, Android Authority reports that HTC will be using this processor in an upcoming 8.9-inch tablet that some believe will be the next Nexus-branded tablet.

Foolish bottom line
Don't expect that the Nexus line of tablets, or something like them, is done for just because Google didn't announce anything new today. While Google no longer needs to convince the market of the value proposition of Android on phones and tablets -- which is what a device like the Nexus 7 was built for -- there's still value in having reference designs that run stock Android.