The 20-year-old scored five goals in 14 League One games for Shrewsbury earlier this term after joining on a four-month youth loan from Palace in September.
And he has now hit a further four goals in three starts since returning to the relegation-threatened League One club.
"Tell me who's better than him in that Under-21 team?" asked Mellon.
"Look at the qualities he has. A young English talent who can score the kind of goals he has for us for so long now.
"He's exciting for the fans and he makes back fours bend with his pace, trickery, directness and his desire to score.
"And he works his socks off. He comes with Premier League standards because that's what he's used to, and it rubs off on everyone else."
Glaswegian Micky Mellon has a deserved reputation for talent-spotting, given the part he played in helping to shape Jamie Vardy's path to the top four years ago.
He signed him for Fleetwood Town on the cheap from FC Halifax in the summer of 2011 before moving him on to Leicester City the following summer, having scored 34 goals to fire the Cod Army into the Football League.
Now he believes that Kaikai, who scored on his only appearance to date for Palace - in the League Cup against Newcastle United in September 2014 - has a lot more to give.
"I want to see a successful England team, even as a Scotsman," added Mellon. "I want to see brilliant players playing for England and I can't believe he hasn't even had a whisper."
Sullay Kaikai's four goals in three starts - including both in the 2-2 draw at Bury last Saturday - mean that he is now Town's nine-goal top scorer.
And, having already helped the Town move eight points clear of trouble in League One, the on-loan South Londoner man admits it is a different Shrewsbury from the struggling, confidence-sapped side he joined earlier in the season.
"The team is now full of confidence," he told BBC Radio Shropshire.
"We go into every game feeling like we're going to win. We're creating lots of chances and it's just about taking them and getting the points.
"We just take each game as it comes and we don't want to get ahead of ourselves too soon. So we'll go into the next game with a winning mentality."
Shrewsbury boss Micky Mellon cannot believe that his on-loan Crystal Palace striker Sullay Kaikai has not been considered by England's Under-21s.