The addition of two more AFLW teams next season is still under consideration after the AFL Commission went against the recommendation of its executive to keep the competition at eight teams in 2018.
St Kilda and Geelong are thought to be front runners for inclusion, with Richmond and North Melbourne pushing hard.
Expanding the women's competition was at the forefront of discussion in Sydney on Friday when the AFL Commission met ahead of this weekend's derby between the Swans and Giants.
The commission is keen to expand the women's game after a successful first season that wrapped up last month, and talks this week centred around the size of the talent pool, possible changes to the fixture and other AFL clubs that could support a women's team.
"There's a commitment to expansion and really the question is whether it's 2018, or 2019. I think you can be definitive about that," McLachlan said.
"Eighteen clubs. That's our aspiration, whether that's a 10-year or a 20-year journey, I don't know.
"We're ambitious. Our ideal scenario at whatever point that is, there are 18 clubs reflecting 18 men's teams, that every club is a rounded club with a men's and women's team.
"We know that's going to take some time to get there but I don't think anyone would have contemplated a couple of years ago that we'd be talking about whether we expand next year from eight to 10.
"Everything's going faster than we'd hoped so you don't want to cap things."
McLachlan was coy on whether an expanded league would mean a longer season.
"At what point do you have a look at conferences, and is that possible, what would it mean for a finals series?" he said.
"The commission was reluctant to make a decision on expansion without actually specifics around a recommended fixture format.
"Lengthening, moving, we broadly think we're in the right spot to do a finals series beyond just a grand final if we could but again it's timing and that'll depend on how many teams.
"There's a lot of moving pieces. We'll look at conferences, we'll look at finals series and we'll come back with recommendations both for eight teams for next year and for 10."
Meanwhile, retired investment banker Robin Bishop has been named as the newest AFL commissioner, replacing former chairman Mike Fitzpatrick.
Bishop, an Essendon fan and a senior executive of Macquarie Capital until late last year, was announced as Fitzpatrick's replacement by recently appointed commission chairman Richard Goyder on Friday.
Goyder also reiterated the commitment of the AFL Commission to appoint an Indigenous member by the end of 2018, but hosed down speculation they'd already been in discussion with retired Swans great Adam Goodes.
"Adam's a sensational person, was a great footballer and you'd hope he'd be one of the people we talk to but I don't want to put any pressure on him or anyone else frankly," Goyder said.
"Adam's been an ornament to the game and we'd want to ensure that all the relationships between the AFL and Adam are positive in the future.
"I think it's unfair to raise Adam in the context of this."