Hey guys, I found a tweak called 'Watchdog', which enables backgrounding on iOS 8.x!
Watchdog is currently in Alpha stage but after testing it, it works quite well, although it lacks some features, it is still early days and the dev has plans on adding additional features and fixing any bugs.
To activate backgrounding, tap on the icon for the app you want to background while in the app switcher, you will notice a small red + symbol appear next to the apps icon, indicating that the app has been backgrounded.
http://imgur.com/zWag9QC
The + symbol will also be present next to the backgrounded apps icon on the springboard!
http://imgur.com/ehwuFeA
If an app is backgrounded, it will auto launch after a restart/respring if the app wasn't deselected in the app switcher first DEB download: https://mega.co.nz/#!61dUWb5T!eQJCPcsSec8cyeN7bz1hbuhLuNXBi5JFNVyUKUfDiNo Mirror 1: https://www.dropbox.com/s/no9houixyjdeph8/com.theronen.watchdog_0.0.1-701_iphoneos-arm.deb?dl=0
If you want to be an early tester, check this out: http://www.reddit.com/r/jailbreak/comments/3czgz7/beta_need_your_help_testing_application/
Video preview: