"It wouldn't be outlandish for them to be at a $1 trillion market cap now," said Mark Mulholland, a portfolio manager whose Matthew 25 fund is among the best performing large-cap funds over the last five years.
But like other portfolio managers consulted by Reuters, Mulholland believes it will more likely take two or three years to reach that level.
Read MoreApple is worth a lotmore than you think
Fortunes wax and wane in the technology industry seemingly overnight; Apple teetered on the edge of financial ruin in the late 1990s and more recently it was partly to blame for the rapid demise of once-storied brands like Nokia and BlackBerry.
Maintaining its spot at the top of the global technology market and growing its now-record market value hinges in part on Chief Executive Tim Cook's ability to keep up the stream of game-changing consumer products launched by cofounder Steve Jobs.
Still, Wall Street appears sanguine in the short term.
After Apple trampled Wall Street's expectations for quarterly earnings in January with record iPhone sales, stock market analysts increased their 12-month stock price targets. Their median average target price is now $134, which is a mere 6 percent higher than Thursday's price and much less than what Icahn says it should be.
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Icahn, one of Apple's ten largest shareholders, said in his letter to Twitter followers on Wednesday that investors significantly undervalued the company and that he hoped the board would increase its share buybacks.
Apple's stock closed 1.26 percent higher at $126.46 on Thursday, bringing its market capitalization to a dizzying $736.6 billion.