Bethell made a compelling first impression during his first Test series in New Zealand, hitting three stylish half-centuries in as many games, with the 21-year-old looking every inch a rising star.
And while that is a huge positive for an England set-up which has made a point of promoting young talent, it could force a tricky decision next summer.
Bethell was only given his chance at number three after an injury to Jordan Cox left England short of a wicketkeeper, with Pope agreeing to step in and slide down the order.
Ollie Pope could be battling for a place in the England team after Bethell's rise. (AP PHOTO)
But with Jamie Smith set to reclaim the gloves following the birth of his first child, Bethell and Pope could be vying for one place next year.
Captain Ben Stokes has previously stated Pope would go straight back in at three, a role where he has enjoyed sporadic highs and several lean spells, but Bethell's knocks of 50no, 96 and 76 appear to have made things less certain.
"He's definitely given us a good headache but we've got a couple of months to work out what we're doing. It's good problem to have," said McCullum.
"We were all a little unsure whether Beth could play at three when we asked him to do it but we saw the talent in him and he has performed very well against a very good bowling line-up. He has a nice bit of class about him.
"He's very meticulous with his preparation and planning which then lets his flair and creativity show on the big stage. We couldn't be more happy with what he has achieved in this series and I think he has shown that international cricket is for him.
"Popey has done really well for us too and to have Beth there as well, you are adding some depth to your batting stocks. They are good decisions and we will not make them in the next few days, when we get together again in a few months' time we will work all that stuff out."
England would not want to cut Pope loose after a year that saw him lead the team four times in Stokes' absence, but a modest average of 33.13 in 2024 does leave him vulnerable.
Opener Zak Crawley has been even lighter on runs, averaging 27.80 in the past 12 months and a torturous 8.66 against New Zealand to end the year on a sour note.
He was dismissed six times out of six by the relentless Matt Henry and showed signs that the pressure was getting to him in Hamilton, reacting with visible annoyance after being given lbw by umpire Adrian Holdstock.
But faith in Crawley appears resolute and there is no suggestion that Bethell's emergence will put him in jeopardy.
"Zak is disappointed with how many runs he scored on this trip but he's got our full confidence. He knows at his best he wins us games," said McCullum.
After two-and-a-half-years in charge of the Test team, McCullum begins work as England's all-format coach in January.
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