Former Wallabies fullback Folau, who has Tongan heritage, had his four-year Australia contract torn up last month for posting on social media that hell awaited "drunks, homosexuals, adulterers" and other groups.
The fundamentalist Christian is fighting his termination in court.
Having played the last of his 73 tests for the Wallabies in November, Folau would not be eligible to play for Tonga unless he sits out international rugby for three years and seeks to qualify for the Pacific island nation's Olympic sevens program.
Kefu, who played 60 tests for Australia, said it would be worth the wait.
"We'd love to have him," Kefu told Fairfax media.
"The next World Cup he’d be available for us hopefully.
"It’s a long time away, so we’ll let the dust settle a bit after his most recent issues.
"We don’t even know if he’s going to play again. He hasn’t indicated where he is going, so we’ll wait until the dust settles and then look at those options."
Folau, 30, also had his contract with Super Rugby team the New South Wales Waratahs terminated for his post, a move that prompted his younger brother John to quit the Sydney side in solidarity.
John Folau, a 24-year-old winger, played one rugby league international for Tonga in 2014 before following his older brother into union last year.
Kefu said John Folau, a fringe player at the Waratahs, was "definitely on (Tonga's) radar" and might feature for the nation as soon as next month's Pacific Nations Cup, which will feature Samoa, Fiji, Japan, the United States and Canada.
"I’ve actually never seen him play but I’ve got a playing history of him," said Kefu.
"You look at what he has done; he’s played in the NRL (National Rugby League) for a couple of years and he’s been on the fringe of Super Rugby for a couple of years.
"He definitely qualifies because he’s got a Tongan passport.
"If he’s played in those competitions before he’s certainly good enough to have a trial for us and then we can see whether he is good enough to be part of that Rugby World Cup squad."
(Reporting by Ian Ransom; Editing by Peter Rutherford)
