Campbell Yule of Cadimage told us on a recent visit to Los Angeles that for their add-ons you only have to pay for upgrades every other archicad upgrade.
So if you purchased an add-on while in AC8, then for AC10 you will need to pay for an upgrade.
If you bought in in AC9, then for AC10 will be no upgrade fee.
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
"Implementing Successful Building Information Modeling"