Items like IK Chest are not subject to the legendary buff at the moment.
They'll allow item level 63 versions of current legendaries and set items to drop and thus buffing all of the current not-max-level legendaries to have the probability of rolling similiar amounts of stats like the 63s we have at the moment.
IK Chest already is item level 63 and thus will not be affected by the change - that's unless they decide to introduce an even higher item level, which is very unlikely.
Mathematically speaking, emerald *should* be better for nearly all Skorn users. Myself and some other monks just seem to do better with the ruby.
In certain scenarios, ruby is better, even mathematically.
If you're running without a gem and hit the monsters with one run-through of TR for 90% of their health (just using random numbers here), it's better to use a ruby to buff your damage, so you do 101% damage in relation to their health instead of using an emerald and leaving 55% of the monsters alive, while overkilling the rest with 370% damage in relation to their health.
When using Bells for Elites/Champions on lower to mid MP, it's a guaranteed 1/2-Shot anyways (and even on higher MPs it hardly makes a difference on the few elite packs), so the gem makes no difference, but as the trash mobs are the thing that you could spend too much time on, if you're struggling to one-hot them you want to make sure, you kill them with one run-through as close to a 100% ratio as possible.
Mathematically, one should be switching the gem to an emerald when doing Ubers or heavy bell runs, but it's really not that big of a difference and I would rather spend my money on some additional crafts - which you do a lot with 40 DEs an hour after all - than on re-gemming every 10 minutes.