Players other than Ovechkin who had a realistic shot at topping 894 goals:
1. Lemieux. With health, he 100% tops it. Probably surpasses 1000+ goals. I think if both Gretzky & Lemieux had healthy careers, they'd have comparable point totals (still lean Gretzky ahead), but Lemieux would have more goals, and Gretzky way more assist. So - this one is obvious.
Lemieux definitely would have had a chance at 900 or more, if health permitted. The only disadvantage for Lemieux is that he gets in only about six prime seasons in a high-scoring period before the League starts to slow down (however, the Pens were still scoring a lot for a couple years after most team weren't, so maybe this isn't such a big deal). Then, Lemieux was around 30-31 when scoring starts to drop. So, his timing was good, but not as good with perfect health, as, say, Mike Bossy's could have been. However, I do think that with all things being equal, Lemieux is the best goal-scorer in NHL history, so assuming good health and
a lot of consistent motivation (which is even harder) he could certainly be #1 in total goals, even well after Ovi.
(I disagree, however, that Lemieux and Gretzky could have comparable point totals. This would only be possible if Mario played three or four more seasons than Wayne. I think Mario had too big of a gap off the early parts of each player's careers. In his first 5 seasons, Wayne racked up 914 points, while in Mario's first 5 he hit 715. He was already 200 points behind by age 23.)
2. Bobby Hull. I think there's a "chance", but I actually don't see it. He might have passed Howe at 801 though. Scoring was low in his prime. He had 610 goals in the NHL after his age 33 season (when he left for WHA). In comparison - Ovechkin had 658 at that age. So for Hull to surpass Ovechkin, he'd have to age better than Ovechkin past age 33, enough to make up ~50+ goals, which to me seems like a big stretch.
Scoring was low in his prime, yes, but when he was still very much in his latter prime (1968 onward) scoring started going way up. There were a lot of bad teams to beat up on from 1972-73 to say, 1980-81, or whenever Hull might have otherwise retired. So, I do think he likely matched or broke Howe's (then) record if he had played through in the NHL. Around 800, anyway.
3. Bossy. I think he's a bit of an unknown. He doesn't contend with the likes of Lemieux, Gretzky or the Hull's for peak goal-scoring to me, but I feel he had the consistency Ovechkin has. It's possible he would have aged well too. In my opinion - if he ages well with health, he'd top 900+, but fall short of 1000 (unlike Lemieux, who'd do 1000+).
I can see the argument both ways for Bossy. His short career was "all-killer no-filler", but his career was also perfectly centered in the highest-scoring / weakest-defense era. Scoring dropped quite a bit in 1986-87 (Bossy was still great, but not quite up to peak anymore), then rebounded for two seasons, and then started dropping pretty regularly from 1989-90 onward. There's also the fact that the Islanders went into the crapper from around 1988 onward, and never fully came out. Would Bossy, a decorated veteran of five Cup runs, have had the motivation to keep striving for 40-goals every year up to 1995 or whatever if his team was awful? If the answer is 'yes', then sure, he had a shot.
4. Brett Hull. With him, it's more about him only starting in the NHL at age 22. If he had started at 18 - and done ~decent, that's 5 more seasons. 894 goals - 741 (Hull's career total) is 153 - divided by 5 seasons, that's an average of 31 goals.
The impressive thing about Hull is that even though he fell far off from his three peak years (which the vocal anti-Wayne crowd always chirp him about, but curiously never apply the same to Hull) as a goal-scorer, he was still really productive right up to almost the very end. In other words, like Ovechkin (if not quite as extremely good), he found ways to adapt his game in order to remain a big scorer. With so much of his latter prime and 'senior' years in the DPE though, I'm not sure how many total goals he could have scored. (As you say, if he'd started at 18-19, then maybe he would have done it.)
5. Selanne. Exact same calculations as Brett Hull. Started at age 22, and hit 76 in his rookie season. If he plays since age 18 in those high-scoring season, he might be able to another 210 goals total. Either way, certainly would surpass 801.
I find this one less likely. Not impossible, but less likely. 1989-90, 1990-91, and 1991-92 weren't hugely high-scoring seasons anyway, and if Selanne was not yet at his physical prime, I don't see him scoring more than 30-40 goals around here. (Also, in Selanne's and Jagr's cases, are we still assuming the 2004 Lock Out? As we saw, that year off had a big resurgent effect on Selanne's career.)
6. Auston Matthews. Age for age - Matthews is ahead of Ovechkin by ~30 goals. Very good chance he can pass 801, and 894 is still attainable (though obviously a very long way to go).
He's already halfway to 400, which is amazing... but Gretzky at his age had about 600. As ever, it'll all depend on how Matthews ages. I think we all know the odds of him being another freak-of-nature like Ovechkin are slim... Matthews is having slightly an off-year this year (still 40-goal pace), but if he can come back strong with another 55-60 season next year, he's looking good so far.
(While we're doing this, we should note that Gretzky experienced injury and work-stoppage, also. These largely weren't in his prime, but we would still be adding on another 50+ goals to his total, which puts him at 944... which means Ovi isn't matching him until late next season at the earliest. Then, Howe's prime was not only low scoring but with shorter seasons. Add on 100GP to his prime years and then keep him in the NHL until 1979 or something... and how many more goals? A lot. We mentioned Hull and the WHA. And Rocket Richard had 50-game seasons when he was very young, and, like Howe, 70-game seasons for the rest of his career.)
To rack up 750+ (or whatever) NHL goals, the player needs these things (besides elite-talent, obviously):
1. Perfect-storm timing / situation (higher scoring and not leaving the NHL, say)
2. Health / Endurance
3. Ability to adapt goal scoring across different eras
4. Motivation to keep at his highest / peak level even in down years or when team sucks, etc.
Richard and Howe didn't have (1). Hull didn't have (1) either because he 'defected'. Gretzky didn't have (3) or maybe (4) (or both) in terms of scoring goals. Lemieux didn't have (2) and I'm not certain about (4).
But Ovi checks all boxes.