When I gave the 1DX2 a run I was not convinced that it was worth the extra over my 1DX.
Certainly the Mk2 IS a better camera but it does not offer me enough to change. The extra fps are irrelevant as I use 10fps max. The high ISO performance is nice and I would like to have it! I wasn't too keen on the revised control ergonomics but a friend (1DX user) thought they were much better - personal choice? Don't like the C Fast slot - simply of no use whatsoever for me - CF is more than fast enough for my wildlife needs/wants. 4K video - they shoot video? No idea how to turn it on and the time spent finding out is a waste of a very small part of my life. Stupid battery change - totally unnecessary and just an excuse to get you spending lots of pennies on packs containing £15 (at most) worth of cells.
The Mk2 is better but not hugely so in the field for my (mainly wildlife) uses - so it was a no go for me.
If you have £2K burning a hole what about trading /selling your 24-105 and getting a 24-70 F2.8 L V2? Been there done it and very happy. You will have change too! The 24-70 V2 makes a big difference on my 18MP 1DX - I can only envy how it would perform on your 5DS. Just a thought.........
Life is for living, cameras are to capture it (one day I will learn how!).