Let me preface this by saying I'm a main with probably 2,000 someodd games on Ezreal, and I've been theorycrafting him with every type of build since S4. (As an aside, please let us insta-buy fully stacked Tear items in practice tool, with the advent of double tear, testing things in practice tool needs quite some time just to even stack) This is going to be a long post, but I'll leave a TLDR at the end.
I'd like to talk about three things for Riot's consideration with the coming nerfs. Firstly, Ezreal's "power neutral" rework, and how it was most definitely a buff, hands down, with no contest, on AD, why that's so, and how it has contributed to the Double Tear build. Secondly, tying into the first, why the Double Tear build is so powerful on him, and lastly, why, because of those two things, the nerfs Riot is seeking to put out are all-out WRONG and will not have the intended effect, and for the most part, won't even nerf him. I will also be offering some suggestions on how to nerf him on AD without nerfing his full AP builds.
Okay, so first up, the rework was a buff. Sure, W's base damage wasn't all that high, but Riot didn't factor in its interaction with Muramana. Since W is a single target spell, it also procs Muramana. It also forces E onto the W'd target, which was previously highly unreliable damage. Therefore, W base damage increase + AP scaling increase + E base damage guaranteed + 2 more Muramana procs guaranteed means you're just adding a lot of instant-pop damage all in one. With the AP scaling increase and more Muramana procs guaranteed, this HIGHLY incentives building double tear, which double-dips into BOTH of those new-found strengths. This allows Ezreal to essentially oneshot once he has completed his Archangel's. Also of note, Bilgewater/Gunblade/Bork active proc a muramana proc as well, meaning once Ezreal has his 4th item, he no longer needs to land Q to kill anyone. W E auto and an item will kill nearly anything that isn't a tank, so anyone out of position for any length of time is just dead if Ezreal capitalizes. This is not healthy, obviously.
Until Season 8, Ezreal needed three conditions to oneshot a squishy. Being ahead by far, a cheesy build that falls off, and landing his ult. Now he can oneshot a squishy with his optimal build, the double tear. It's so powerful right now because giving him two extra Muramana procs guaranteed and higher AP scalings means mana + ap = good. This means Seraph's is just too powerful for this, and these intended nerfs are actually all wrong, they will buff him unless he is dealing with someone that is far too tanky to burst, and his Q poke will be too low if they have any sustain to deal with him. The W buffs then mean EARLIER oneshots, because W at rank 2 with the "nerfs" are going to be W at rank 4. Ezreal also does not need his ultimate to do any of these oneshots, and the only time he really NEEDS his ult for damage is pre-Muramana, so you only nerfed his early game without touching on the strength of double tear, which is the issue. The only thing the Ult nerfs do realistically is slightly weaken the pre-18 minute fights and weaken his already garbage wave clear. The W buffs just increase his ability to oneshot someone and decrease their chance to play against it, and weaken Ezreal in spots where he's already weak, such as trying to kill someone tankier where he'd need more consistent Q damage.
Alright, now that we've got why Ezreal is strong and why the nerfs are in the wrong areas, here's some right areas to be looking.
Like I said, the rework buffed his burst through the roof. A lot of people like playing AP Ezreal, and they seem to be trying to balance around this as well, so then, why not nerf Muramana a bit? Introducing a lockout cooldown to Muramana's passive damage is the best way to negate Ezreal's burst and disincentivize Double Tear builds, though, to be honest, it'll probably still be the go-to build, it shouldn't be able to oneshot anymore. At the moment, Q W E Auto Q gunblade/bork auto takes about 1.2-1.4 seconds, and hits SEVEN Muramana procs. Adding a lockout on Muramana passive damage hurts no one in the process, namely not AP Ezreal or other Seraph's builders, and only mitigates AD Ezreal's burst, while still maintaining his strengths in the areas he was designed for: His poke. If you add a cooldown on the Muramana damage, he'd need some compensation buffs, though, since he would not be able to kill tanks as easily, either, which he already struggles at. For this, I'd suggest giving him more attack speed per level. Base attack speed buffs would make him a viable jungler again, which I know Riot doesn't like, so giving him more attack speed per level means by the time he gets Muramana, he has enough attack speed to compensate for the lack of Muramana procs in all-out fights to equalize the damage, less burst because of less Muramana procs in a 1 second period, and it won't hurt anyone because no one else builds Muramana.
Edit: I'd suggest either the same or half CD as a lockout period to Sheen to further disincentivize double tear's 45% CDR, since 35% is a happy amount of CDR to hit Q's on CD with to proc sheen that no one cares about since Muramana's damage is too high, and Ezreal players already have Sheen's lockout ingrained so it won't feel clunky trying to line up sheen and Muramana damage at the same time.
Another thing that could be done is to simply add a base damage centered around where Muramana with just one sheen in tow is, and then nerf mana scaling on it, but this is a far trickier route because of the aforementioned 7 procs in about the time it takes for anyone to register Ezreal has even gone in, and Ezreal currently only needs ~4 to kill anyone who isn't stacking resists/has Sterak's if he's not ahead, and 3 if he is.
Ezreal "power-neutral" rework made Muramana and AP way better at dealing damage, so buying Seraph's is a no brainer that oneshots things. Nerfs don't address that. Lockout/internal CD on Muramana damage w/ compensatory attack speed per level buffs fixes his ability to oneshot while not hurting his overall damage.