The plan for the 787 has always been to make the aircraft engines "plug and play". It's not just the pylon, it's all the other system connections (for example Rolls has an inlet P2 probe heated by aircraft electricity - ~500 watts - that GE doesn't need). As Torquelink notes, it helps the resale value to be able to swap between GE and Rolls.
A couple years ago I asked a co-worker who was on the 787 if they'd actually made the plug and play work, he said it wasn't certified but didn't know why (or if there was some sort of showstopper that would prevent it being certified). I haven't heard anything further (and since I'm now retired I'm pretty much out of the loop).
The Ice Crystal Icing issue on the 787 GEnx-1B was cleared about 2 years ago with a FADEC software change. A similar s/w change was incorporated on the 747-8 GEnx-2B which cleared it for ICI up to 35k. To clear the 747 for ICI up to the 43k service ceiling requires a hardware change which will take a few more years to circulate through the entire fleet.