spoiler
I watched ALL OF IT! All episodes, filler, OVA, specials, Movies, manga cover stories, even the dub voice actor blooper reel.
So many fantastic moments, "good" filler and "bad" filler, side character plots continued in the cover stories, the discussion on this stuff is limitless.
If you have a favorite moment, an OVA you really enjoyed and wished was canon, a movie you didn't think worked, an underappreciated character you need to discuss, the best parts of the soundtrack, anything at all, let's talk about it!
Note: Even though I watch the sub and dub interchangeably, I stopped at 1096 where the dub arc is currently halted at. I found that, without a ton of free time to dedicate to the show, I was able to still squeeze in a few episodes during my weight-lifting workouts to keep progressing through it. It's easy and surprisingly motivating to lift weights to the dub, but near impossible to accurately read the subtitles during intense sets. That said, impatience might cause me to trade sleep or other shows/games/social-stuff for time to watch the subbed 1097 and beyond instead of waiting for the dub.
PSA for new adventure seekers: For anyone like me that loved the anime as a kid but was massively intimidated by how big the growing episode count for one of the longest running shows in history has gotten to now, let me say that you can catch up and it is absolutely worth your time if it's something you truly want to see. I did things the "hard way" but you can skip the filler, drastically cutting down the episode count and fixing the pacing, and experience an adventure unlike any other. (If the earlier stuff still feels like a slog, maybe wait for the reanimated early seasons that Netflix is putting out).
At some point I'll post one of those chronological/recommended watch order lists with all the specials, movies, cover stories, etc., put in reasonable timeline order with the main arcs.
Very interesting question, I've thought about this now for a good while so apologies in advance for how long this might get.
We've gotten about 25 years of One Piece so far with 1136 episodes currently. Oda turns 50 in a few months in January. I don't know if it's probable, but I think it's very possible that we are at about the halfway mark. Just based on gut feeling, I'd guess Oda wants to see what else there is in this wonderful story world for at least 20 more years, maybe even 25-30. I'm thinking there could be somewhere around 2000-2500 episodes in total, but also that there is no way Oda could keep up the current pace for the remainder of that.
I'm pretty sure he still lives away from his family during the busiest parts of his working season right now, only going back home during breaks and holidays. I think it's actually possible he could keep that up for the next 15 years until he is 65, but that he'll want to be able to lighten his schedule and live at home with his family after that.
That said, I think he'd still probably love writing this thing even at that point, up until maybe 80. We'd probably see more filler and longer breaks to make up for a reduced pace (a welcome price to pay in order for Oda to live at home) which is why I think episode counts could get higher.
A tangent here, but I remember some celebrity in an interview talked about a party that their friend had every year in order to explain a story they'd been writing since the 4th grade. This person had created a story world when they were a kid that just kept growing for decades even until the present day. They tried to write a book, a screen play, an outline, but every time it was just insane trying to write out thirty years of a growing story universe into anything that made sense. But people got into it when they tried to explain it, so it turned out the best way to tell the story was to just mention a part of it and let people ask questions which then were clarified with the intricate details and history and culture and laws of this world, etc., all at a party every year.
I think Oda is a lot like the person that throws that party every year to try and explain a bit of their vast story world. But, instead of having it build up for decades without record, Oda's story world had been written and published from its very beginning. I think the world of One Piece is part of him and he just keeps imagining it as time goes on. When we daydream about things, whether it's winning the lottery or being able to fly or whatever, I think a lot of Oda's daydreams are the world of One Piece and that it's constantly growing in his imagination.
That's why I think he'll keep going and we'll get a total of 40-55 years of One Piece. I'd even imagine some kind of comic strip style continuation or co-running a spin-off after that because it's that much a part of him. However, it also is true that Akira Toriyama just died at 68. While I realistically think Oda could do this even longer for a total episode count of 3000, I don't know if he'd risk the possibility of not getting to see Luffy reach the final island before he dies. Therefore, my guess is he does a 2000-2500 episode total with maybe bonus stuff set in the same world after in some form.