I took in the fact that you can proc the passive with e-q-q but also accounted for that Ekko won't blow people up instantly from that combo, he needs to auto attack after getting in range with his Phase Dive to trade and go all in so I chose Nashor's for extra damage while he's autoattacking.

I feel the Leblanc vs. Ekko Lane is a tad bit in Leblanc's favor but not by much. Ekko can basically nullify her E and and jump in on her with his Phase Dive. Ekko can also chase down Leblanc with his multiple slows. Leblanc can W out of Ekko's ultimate, which is a big drop in power to him since his greatest AP ratio is off of it. Leblanc can also easily get out of his Parallel Convergence. But since these both have high burst at mid and late game this lane is pretty explosive for the both of them.
Ahri vs. Ekko Lane in my opinion favors Ahri throughout the entire game because of her high mobility. She can easily ulti out of Chronobreak and Parallel Convergence. And since Ekko requires to be in the enemy's face to deal his damage a simple Charm can ruin his engage. Late game the Charm combo will simply blow up Ekko.
Karma vs. Ekko lane would probably be very annoying for Ekko. Although he can dash out of her Q I agree that if he attempts to burst her down she'll just shield and outdamage you. I think the only way he will be able to kill her is either when both of their damage is very high or when Ekko comes back from a roam and Karma is pushed up and Ekko can use his Chronobreak to break the chain but also do damage to her. I think the only way he can kill her is by getting his ulti damage into the mix.

I use this exact build, before anyone even posted any guides. I'm glad someone else thought Nashor's, too. I would like to try Tri-Force though and compare the two, but I do like Nashor's more. I didn't even think of Guinsoo, thank you so much for putting that there, I feel like that is a great option for when you're ahead, excellent specs on it. Going to try that now, if I ever get a change to use him in Normals... Lol, autolocks and bans.

But how do you feel about match ups? I have a few ideas about some champions, I'm not a ranked player (I are scared... will try eventually just worried about bringing the team down), but I feel like these are legitimate ideas.

LeBlanc: Ekko should have an advantage over LeBlanc as long as he is quick and can combo his abilities well. When LeBlanc is about to initiate an assault on you, she will get into range to Q you. Around level 3 or 4 (the recommended levels for taking your W), you can shut down her early engages. When LeBlanc comes into her Q range and you suspect an attack, trigger your W. Because LeBlanc is so quick and bursty, this will ensure that when she charges you with her W, by the time she reaches you your W will pop and when she lands on you, she will be stunned, allowing you to fully combo on her. This also helps you avoid being ganked if she's going in intending her jungle to follow up. Ekko's E also dodges LeBlanc's E and gives him a good engage. Then his Q is a lengthy poke not inhibited by hiding behind minions And the slow is enough to make her unable to initiate without the likely-hood of dying. LeBlanc must play passively against Ekko, merely poking and farming while waiting for her jungle to gank.

Ahri: Ekko will have a hard time dealing with Ahri pre-6, before it changes to a skill match. At early levels, Ahri has great mobility and evasion compared to Ekko. She also combo's much easier than Ekko if he is caught out of position. Pre-6 Ahri can shut down Ekko's combos with a well timed charm, after or before he dashes. Because Ekko must E just before or just after his E pops, Ahri will know what he is about to do when the zone becomes visible, allowing her to either dodge entirely by firing Q before it pops, or shut down Ekko's dash by hitting him with charm. Even if Ekko is able to dash in first, if Ahri hits him with her charm Ekko will be unable to fully combo in time. The only good thing in this situation is that neither champion can combo hard on each other, stalemating. Post-6 things become a skill matchup. As long as Ekko keeps moving, he can crush Ahri with his ult, but this will be difficult still since Ahri will expect you to ult when you get low on health. If her ult is up she will simply ult away and back or simply go for an all in and burst you down before you can ult. Her built in sustain and the movespeed boost from her Q and her ult charges give her enough slipperiness to dodge all of Ekko's abilities or outrun him. She can bait out his abilities to force him out of combos, and she can punish him for closing in by using her W. Despite this, Ahri is still vulnerable to Ekko's high burst damage and she can be caught easily if her ult is down.

Karma: Although Karma is mostly Support, midlane Karma is very powerful and has great CC that inhibits Ekko's engages. Her Q poke deals great damage, which makes her pokes dangerous and fantastic for farming. This forces Ekko to keep a range, limiting his csing. This gives Karma an earl harass factor against Ekko. Her kit is also a lot of trouble for Ekko. Because her tether isn't canceled by Ekko's stun, she can activate it when you try to go in on her for a combo, rooting you and keeping you from escaping. Her ult+Q and ult+W make her very hard to fully in her, and her shield can mitigate much of the damage you'll try to do. Although the burst is extremely high, Ekko may or may not be able to kill her in a full combo. Because of these factors, landing a stun is CRUCIAL for Ekko to burst Karma down. Because her tether simply roots, if Ekko is able to use the teleport factor of his dash before the root procs, he can basic her down and finish her with a Q when she tries to escape. The danger of this, however, is that if her jungler comes in at this point, if you don't have your ult up, you have no escape.

Done, thank you for the suggestion!