New Snapdragon 415 an 425 offer mid-range performance features
Qualcomm's product line has been somewhat inconsistent recently, with products from a series for a certain segment actually being used for a different segment. For example, although the Snapdragon 410 SoC is the mid-range 400 series, it has actually been deployed in significant numbers of cost-sensitive entry-level 4G segment devices.
There used to be a gap in Qualcomm's product line, large in terms of performance level, between the lower mid-range Snapdragon 400 and the premium level Snapdragon 801. Not too long ago, Qualcomm addressed this gap with the mid-range Snapdragon 615, featuring a total of eight Cortex-A53 cores, four with maximum frequencies in the 1.5 - 1.7 GHz frequency range and four clocked lower (e.g. 1 GHz) for lower consumption. With the new Snapdragon 415, Qualcomm is bringing a SoC similar to Snapdragon 615 to the cost-sensitive mid-range segment, largely replacing the Snapdragon 410 for that tier (as I have discussed previously, Snapdragon 410's performance is flawed in several ways).
Snapdragon 415 could be a rebranding of 615 to replace 410, or maybe not
In fact, there is a possibility that Snapdragon 415 is actually the same chip and in fact a rebranding of the same product. Both Snapdragon 415 and Snapdragon 615 have a roughly similar CPU set-up (eight Cortex-A53 cores), an identical GPU (Adreno 405) and a Cat 4 LTE modem. Although Qualcomm in its press release mentions commercial availability in end-user devices for new chips will happen the second half of the year, if it is the same chip it is likely that Snapdragon 415 will appear earlier (since it has essentially already in production for some time as Snapdragon 615), replacing Snapdragon 410. However, in its specifications page for Snapdragon 415, Qualcomm does not mention any distinction in CPU speed between cores, making it likely that it can run all cores at the maximum clock frequency, similar to MediaTek chips already on the market.
Meanwhile, Snapdragon 425 has a CPU configuration similar to Snapdragon 415 with a higher maximum clock speed, and also the same GPU, but has a more advanced modem with Cat 7 LTE, and better ISP functionality for camera processing. A comparison can be made with MediaTek's MT6752 which also has a 1.7 GHz octa-core Cortex-A53 CPU (Snapdragon 425 probably also drops the pseudo-big.LITTLE design of Snapdragon 615). Given the clock speeds, it is likely that Snapdragon 425 is manufactured on a higher performance process than TSMC's 28LP, most likely TSMC's 28HPM, like MediaTek's chips.
Symmetric octa-core CPU configuration has advantages for multi-threaded applications
Although "LITTLE" cores in a big.LITTLE configuration can be taken advantage of in multi-threaded algorithms, most applications and algorithms are designed for and work best with processor cores running at a comparable speed, distributing the workload evenly between cores, favouring symmetric CPU configurations in which every core can run at the same maximum frequency. This shows in the very high multi-core benchmark scores of chips using such a configuration, such as MT6752. It looks like Qualcomm is quickly moving towards such as symmetrical octa-core configuration (pioneered by MediaTek, which already has comparable chips on the market) for the cost-sensitive part of the market, up to the mid-range segment.
Snapdragon 415 and 425 not likely to be cheap in terms of manufacturing cost
Although the eight Cortex-A53 cores are relatively small so their consumption of die space is relatively limited, as I discussed earlier the Adreno 405 GPU, with its medium-level performance, appears to have characteristics of a GPU targeted at higher-end segments (in terms of ALU/shader performance, for example) and is likely have a relatively large die size in relation to the cost-sensitive segments it is addressing. Because of that, Snapdragon 415 seems to be somewhat of a stop-gap measure to replace the successful, but flawed in terms of performance, Snapdragon 410 SoC, as the gross margin on this chip could be relatively small.
The proliferation of chips such as Snapdragon 415 likely to continue Qualcomm's heavy reliance on TSMC's 28LP process, which is lower-performance process technology than 28HPM. Why Qualcomm would place such emphasis on this process for smartphone SoCs is unclear, since the advantages of the 28/20HPM process are very desirable for smartphone SoCs for everything but the entry-level segment, and competitor MediaTek has adopted this process for most of its range. Qualcomm has been using 28HPM and 20HPM for its Snapdragon 801, 805 and 810, although the it is likely Snapdragon 425, 618 and 620 will also be using it.
Little heard from quad-core Cortex-A53 Snapdragon 610
It would have made sense if the Snapdragon 610 (announced as quad-core Cortex-A53 CPU and the same Adreno 405 GPU as the products discussed above) would have trickled down to the 400 series. The fact that this chip has barely appeared on the market and that it is not mentioned in the press release suggests it won't come to market at all, perhaps due to technical problems with the chip or as the result of a strategic decision. An updated quad-core Cortex-A53-based solution would certainly make sense in Qualcomm's product line.
Snapdragon 618 and 620 have premium-level characteristics
Qualcomm also announced two new performance segment processors, Snapdragon 618 and 620. These are the first announced mobile chips to feature the new Cortex-A72 processor core from ARM, which is an improved version of the high-performance Cortex-A57 processor core. Snapdragon 620 has four Cortex-A72 CPU cores clocked up to 1.8 GHz and four Cortex-A53 cores up to 1.2 GHz in a big.LITTLE configuration, while Snapdragon 618 reduces the number of Cortex-A72 core to two to provide a better balance in terms of cost.
Although on the surface the model numbers of these new SoCs may seem close to Snapdragon 615, their specifications suggest that they are targeting a significantly higher performance segment. The memory interface is a dual-channel interface supporting LPDDR3 up to 933 MHz, clearly a defining feature for a high-end product, and making the support for QHD (2560x1600) displays a sensible feature. They also feature a new, "next-generation" GPU.
In short, despite their model number, Snapdragon 618 and 620 have little to do with Snapdragon 615 and should be thought of as processors in the same segment as processors from the Snapdragon 800 series such as as the Snapdragon 801 and Snapdragon 808. If and when Snapdragon 808 (with two Cortex-A57 cores and four Cortex-A53 cores) will appear on the market is unclear (some test results have appeared in the Geekbench database), the new announcement might suggest that it will quickly be superseeded by Snapdragon 618.
Sources: Qualcomm (SoCs announcement)
Updated February 26, 2015 (Edited and expanded to reflected likelyhood that Snapdragon 415 and 425 use a symmetrical CPU configuration, not pseudo-big.LITTLE like in Snapdragon 615).