I could, probably yes.
But would i? Absolutely not, the standard UI is horrendous, AH impractical even after rework, bossmods are just nice for the first 5-10 pulls until you get into the rhythm of the fight and WeakAura’s are just handy dandy to track the five billion things you gotta track (obvs im overexagurating things abit with the WAs).
I could , As I have in the past, However I’ve got that used to having certain addons that it would take awhile to adjust.
I currently use 32 different addons…
Deadlybossmod for LFR.
TomTom for when I need to fly around checking to see if something is spawned.
All other times? Not really. Just those cases.
Can you? If you’re a high end player, No. You can’t.
If your definition of end game content is LFR raiding? yes. You can play without addons.
Overall, playing without addons is like having all sorts of available for free equipment around, and then deciding on using your fist for breaking and eating a coconut. It’s doable, but Why would you?
To an extent yes but in a raid environment unless we go back to simplistic mechanics like Vanilla then no it’s not really practical.
Some addons are purely QoL, others give useful data/infornation.
I always play with no addons, bar TRP3.
While I don’t clutter my game with countless addons, I do use a few important ones and also a few roleplaying ones, which in themselves, are the most important.
Tried few of them, but it really isn’t my thing… Can’t stand to see some1 having cubes ( health bar, enemy names etc ). Like the game how it is and was from the beginning. Maybe I could get this add on that allows you to sell all the junk from bags. Think that’s useful 
Leveling: ZygorGuidesViewer. The waypoint system has helped my poor navigational skills a lot, and I could not have completed these many zone Loremasters without it. Never parting with it.
My level of endgame content (<15 Mythic+, LFR/Normal Raids): WeakAuras, BigWigs, ElvUI. Maybe? I could go without my WeakAuras, and sometimes the UI I set up in ElvUI randomly decides to disappear. BigWigs/DBM though, are very helpful. I could begrudgingly do without those but not without irritation.
Other AddOns I have: MogIt, Bagnon, Details, Pawn: Could do without all of these. But they have greatly improved my world content experience (especially MogIt - never can see the new pants appearance I got in the Dressing Room with Robes on!) and losing a couple of these would make me sad.
Overall, I could play without the AddOns I use. But I see no need to remove them for the sake of some “purist” experience. If Blizzard decides to one day close the APIs I might relegate my playing to very little content. It worries me little that I rely on them - I choose to rather look at them as crutches to shortfalls of my skills, allowing me to do better.
I could, but I don’t use many addons to begin with.
Usually only a few for raiding and dps meters and such.
If all addon support was removed tomorrow, I probably only would have missed a few QoL addons. Bagnon for example. I use a lot of others, but none that are absolutely crucial for my gaming experience.
I am exactly like you, the core UI works just fine for me.
But there’s no way I can live without the addon All The Things! I have a very addictive relationship with this game… 
I’d say the absolute must addons are Details!, DBM and Bigwigs. I also use the scrapper addon for convenience when vendoring trash. You can totally go without DBM, but Bigwigs is needed for cooldown tracking on raid bosses.
Details is needed, especially for dpss to know how well you’re doing, and it also helps you track who is running flasks and food XD
Could I? Yeah!
Would I? Hell nooooooooooooooooooooo.
have been thinking about this since the takover of curse. I only use 2 if blizz gave coords i would scrap that one, which leaves Pawn which I need cos Im a dummy and like the green arrows telling me what to do.
Only if i played DPS.
I would pretty much quit if i had to play Tank or Healer without addons.
Without DBM the game becomes largely unplayable to me. I need the wake up and pay attention alerts because the game itself just is not clear enough with boss mechanics.
Just look PVP, you can choose to go without addons, but then you will be gimped compared to other players, because their addon will show them exact second of enemy cooldown, without addon you will need to play 1000 hours to be able to guess when enemy have something. So addon litelary turn noob into pro.
In other games its not strange than devs approve / disaprove addons, I think WoW reached this point where some addons go to far. This will need to happen in WoW soon or later.
Wows base ui has remained largely unchanged since vanilla and its awful…
Everything is too spread out (actions bars) too small to read easily (unit/party frames) or moves around to quickly to track (buffs debuffs)
This largely is why many people rely on bartender / weakauras etc.
I find many of wows later ui additons are perfectly up to the task (raid ui, name plates) … just that base really needs some work
I would have NP playing without addons, the only addon I would REALLY miss would be my bagaddon though 
AdiBags is just so handy as it also shows currency
No. The raid mechanics seem to be designed on the assumption of add ons and I couldn’t handle them without 