There are times when Xcode chugs on a top of the line 2015 15" 2.5Ghz rMBP with 16GB of RAM and a 2GB/s PCI-E SSD. Not frequently mind you, but it does happen. It's incredibly heavy and I can't see it being usable on an iPad unless Apple manages to magically pull out an A-series CPU that's in the same class as a Haswell i7.