My top 10 greatest goal-scorers of all time are:
Tier 1:
Ovechkin/Gretzky/Lemieux/Bobby Hull. That's the top 4, probably in that order, but could probably be argued among the 4.
To me, there's almost no chance Matthews reaches it. Why? Because it would require ageing as well as Ovechkin as a goal-scorer. Is it possible? Sure, anything is possible, but seems extremely unlikely. Most of all - it's simply too soon to tell. It won't be until he's age 30 and 31 and 32 that we'll get a sense of if it's possibe or not.
Tier 2:
Maurice Richard/Gordie Howe. They are #5 and 6, again in that order, though could probably be inverted.
Again - very unlikely Auston Matthews will reach or surpass either of them. It's a bit more attainable than the top 4 maybe, but he's still very far away, and unless he ages like Ovechkin or very close, he probably doesn't reach this high.
Tier 3:
Bossy/Brett Hull/Esposito/Bure. Probably in that order for slots 7-10.
To me - this is the tier Matthews is most likely to reach. Not only that - but I'll say he will certainly displace Bure all time for #10 in my book, short of some career ending injury very soon.
Esposito/Hull/Bossy will be harder to surpass. I think it's possible, but it's on the upper end of likelihoods.
Bossy had a short career maybe, but his strength is not only regular season but also playoffs. Which is also Matthews's greatest weakness so far. Even as a goal-scorer, he is quite weak for playoffs - he'll have to put up some more numbers there if he wants to climb ranks all-time.
Short answer - I have no idea where Matthews ranks today, but he will almost definitely finish at least #10 all-time for me. #7-9 is also plausible, but harder. Anything higher is quite unlikely, though not impossible.