Ennis-Hill won Olympic gold with a national record score of 6,955 at London 2012 and claims her next big target is to become only the fourth athlete, after Jackie Joyner-Kersee, Carolina Kluft and Larisa Turchinskaya, to break the mark.
The Olympic champion has spent most of the year sidelined with an Achilles injury and, in her absence, 20-year old Johnson-Thompson finished fifth at the World Championships with a personal best 6,449 point score.
“Kat is extremely talented and she’s been improving year on year, so she’s got lots of time to develop as an athlete. I’m sure eventually she’ll get that British record, you don’t have it forever unfortunately," said Ennis-Hill.
“She’s really close to a podium at one of the major events. I think the World Championships were a good championships for her, she had some great personal bests and came away with fifth place.
"I know she was a bit disappointed with that but she has got so much time, she’s still young and has a lot to develop within her events."
Johnson-Thompson - who is expected to be Ennis-Hill's biggest rival at next year's Commonwealth Games in Glasgow - was just 28 points off a medal in Moscow this summer but insists she has time on her side.
"I will only be 23 in Rio and that's not an age when heptathletes really peak," she said.
"2020 is realistic for me but it doesn’t mean I’m not going to try and win an Olympic medal in Rio.”