iMacs identified as "iMac15,1" and "iMac15,n" were found by Pike's Universum in the ".plist" files for power management in the latest OS X beta. These identifiers suggest a new generation of iMac, as the 2013 desktops were identified as "14,1," "14,2," and "14.3."
In addition, AppleInsider was first to discover earlier this week that estimated shipping times at Apple's online store for new iMac purchases had slipped to between 3 and 5 business days, down from the usual turnaround of 24 hours. Authorized Apple resellers are also seeing low inventory of current iMac models, all typically good indicators that an update is forthcoming.
The timing also lines up with claims from well-connected analyst Ming-Chi Kuo of KGI Securities, who has indicated that Apple may be planning to launch a new low-cost iMac model in the near future. With Apple's WWDC keynote set to be held next Monday, it would seem to be an opportune time for Apple to unveil a refresh to its desktop lineup.
It's believed that Apple may be preparing a cheaper model to better compete with Windows-based all-in-one desktops from HP and Lenovo. Currently, the iMac starts at $1,299 for the 21.5-inch model with a 2.7-gigahertz processor.
Kuo's report only mentioned a more affordable iMac, and did not suggest any major changes may be coming to the rest of the lineup. Therefore, it's possible that Apple may simply update the systems with faster Intel processors, and potentially sell the machines at more affordable prices.