If I buy the D7.1.4 prime license today and have some modules from Boonex market installed, and then D8 is release, will I still be able to upgrade to D8 with all existing functions?
Dolphin Classic is not directly upgradable to Dolphin U. They're very different. Your license, however, would work for either Dolphin. That means that if you have Dolphin Classic now, and at whatever stage decide to switch to Dolphin U, you would be able to download any Boone-made extensions free of charge.