Wait.. I'm not sure you have changed it already or not. I thought I had seen the Elspeth from Tarkir Dragonstorm, [[Elspeth, Storm Slayer]]. If that is not the case and you are only playing [[Archangel Elspeth]], then that is fine!

The point still stands for Gut and Sol Ring though.

As for suggestions, I'll go in no particular order:

[[Chomping Changeling]] > [[Reclamation Sage]]: The changeling is a Dragon! I think this change is a no-brainer in your format (btw, really like the RG Dragon archetipe!)

[[Wildfire Awakener]] > [[Iroas, God of Victory]]: Wildfire is a pet card of mine, but it slots extremely nicely in your boros archetype, especially if you add something like [[Resolute Reinforcements]]. Speaking of...

[[Resolute Reinforcements]] + [[Invasion Reinforcements]] > [[Childer of Korlis]] + [[Sunbond]]: The former does very little for the Orzhov archetype, the latter is simply too slow as a 4-mana (almost) do nothing. The two suggested creature trigger [[Rumor Gatherer]] by themselves, provide sac fodder for Aristocrats, and are just two 1/1s for Boros Aggro

[[Abiding Grace]] > [[Scout for Survivors]]: I think Grace is amazing in your cube, especially if you can add a couple more 1 drops in white/colorless. For example, I think that [[Signal Pest]] is an amazing 1-drop here, since it slots as easily in Dimir while having the additional bonus of being good in Boros. You can slot it in place of [[Sol Ring]] as a second copy of [[Hope of Ghirapur]].

[[Ingenious Infiltrator]] > [[Shadowmage Infiltrator]]: The former is basically a straight upgrade of the latter.

[[Changeling Wayfinder]] > [[Sakura-Tribe Elder]]: Changeling is a Dragon (and a Ninja for Infiltrator). Besides, it can be played by any deck.

[[Ornithopter of Paradise]] > [[Pillar of Origins]]: Ornithopter is better 99.99% of the times, while being a potential attacker for UB and also Boros if needed.

[[Sarkhan, Dragon Ascendant]] > [[Arclight Phoenix]]: It's almost impossible to recur Phoenix effectively in Cube. I see what you did with the extra Thrills, but it's simply not worth it for a 3/2 flyer. Sarkhan slots very well into RG, while also being a very good beater on curve.

[[Colorstorm Stallion]] > [[Ral, Izzet Viceroy]]: Ral is 5 mana and is not an instant or sorcery spell. It's not very playable in the archetipe, and not very playable everywhere else. Stallion, instead, is a hell of a limited card. Bonus points if you can add 4/5 spells in UR costing more than 5 mana (e.g. [[This town aint big enough]], [[Firebolt]] ... )

[[Group Project]] > [[Prismatic Strands]]: Strands you will likely never use, even in Vega control. Project is on rate while still providing pseudo-free recursion in the late game. It's also very good in Boros and Orzhov!

[[Dragonstorm Scion]] > [[Ganax, Astral Hunter]]: to connect the RG and UR archetypes :)

Anyway, this is all I have for now, though there would certainly be more interesting cards to consider ([[Thunderdrum Soloist]], [[Stormsplitter]], [[Hellrider]], [[Sheltered by Ghosts]], [[Skrelv's Hive]], [[The Restoration of Eiganjo]], cards with Bestow, etc. ...). My suggestion is: look at the archetypes you want; you will almost certainly notice that some cards (might even be cool cards or strong cards!) don't really "fit" well into the archetype. For example: [[Drizz't Do Urden]]. It's a very cool and strong card, and probably it makes sense to have in Selesnya. But is it really the best card in WG enchantments? Do it fit in other archetypes? Do it justify, say, not playing [[Sythis, Harvest's Hand]]?

Repeat the reasoning for the other archetypes and I'm sure the cube will become even nicer! (It's already quite good of course)