Only two top-flight clubs - Hull FC and Wakefield Trinity - are running a second string side in 2019 despite many critics insisting it should be enforced that everyone does so.
The RFL says it supports reserve grade rugby - otherwise players can be lost from the game after Under 19s - but it is up to the clubs to decide.
Many clubs have opted against it due to financial reasons or others have changed their minds due to the dwindling number of Super League rivals involved.
Asked whether Super League will take control and insist all its members runs such a side, Elstone said: “The honest answer is that we’ve got an 18-month focus on getting the best broadcast deal.
“Creating fantastic youth development pathways is not going to impact in that window. “But for the long-term prosperity of the sport, we need to get more people playing and more to the start line as a professional Super League player.
“Everyone should be keen to ensure we do that as well as we can.
“The reserves debate is a complex one; the equivalent in football, the under-23s, has had huge investment and I’m still not certain it’s making a huge difference.
“It’s complicated and reserves may be part of the solution, it may not. But the game as a whole needs to address that.”
Elstone, of course, was Everton CEO before taking over at Super League last year.
He has also said the competition could start next year with a Nines tournament as the sport seeks to create more ‘events’ to attract new fans.
Looking at the 2019 calender, Elstone admitted: “There’s nothing imminent in the pipeline but we’re conscious there’s a potential plateauing of events after Magic in June and July before the play-offs.
“There’s a window there where there isn’t a real spike, so we’re looking at things we can do to create a few spikes.
“We had some serious talks about a Nines tournament for January 2019, and that fell away due to a little bit of short notice and funding.
“But we’re talking to that same promoter about Nines for January 2020. That’s early days though and there should be no expectation that will happen.”