You should check out this thread, starting here about what the new V2 IQ brain can do.
The biggest stumbling block for me is connecting motors. Arduinos need motor boards. Most of them are only good for 1 AMP without being hugely expensive. VEX IQ has been a problem in the past because of the way I2C was set up. This seems to have gotten turned around with the new brain.
Now the next stumbling block is the wonky RJ connector. Finding them and crimp tools is hard. It would be nice if VEX would sell packs of the connectors.