So for 
UNIQUE – SPELLBLADE: After using an ability, your next basic attack (on-hit) deals 100% base attack damage and 30% ability power as bonus magic damage (1.5 second cooldown).
VS
New item introduced that replaces Enchantment: Runeglaive.
+60 Ability Power
+10% Movement speed
UNIQUE Passive - Echo: Gain charges upon moving or casting
At 100 charges, the next spell hit expends all charges to deal 80 (+10% of Ability Power) bonus magic damage to up to 4 targets on hit.
Idk, for Raw burst it will still work with Eve, what she does lose out on is sustained damage depending on how fast she an refill this. Runeglaves helped her in long term fights since she can proc it a lot, even early on.
What does she lose? Spellblade passive and 10% CDR.
What did she gain? 20 AP and 10% movement speed.
20 AP means she will gain 27 more damage on her abilities per cast, 33 at level 9.
Typical Evelynn runepage for most people is,
Flat AD reds.
Flat AP Blues
Flat Armor Yellows
Flat AP Quints.
25 AP from there about, .83 per level from masteries usually. And she will have Thunderlords or Stormraider , most likely Thunderlord. 80 base damage + 10% AP from that item On spell cast Two more hits and she gets thunderlords proc'd. It's own base and scaling off her stuff.
New one gives her better sticking power and stronger upfront burst, til later in the game when runeglave catches up with the spell. New item is a stronger in slot item than runeglave outside of the passive part which is still mixed on strength in different areas.
I think she will like the 10% MS more overall to slip in faster than before and she will have more upfront burst.
I don't think this will nerf her honestly, if it does it won't be much. 20 more AP and now 10% MS means she is harder to shack off and her roaming is way stronger.
The biggest hit is her sustained damage from this, but it won't hurt as bad given how this items helps her spells do more damage. Recent buffs to the cunning tree will also help her a little bit.
If it really turns that unappealing to her, it might open up
builds again. I've mostly gotten into Eve at the end of the season and this is what I have looked at so far and have played her as my main jungler for a while.
I don't think this is hurt her that much if at all, since she is also gaining from new changes as well.