SPAS-TESHILOVO, Russia—The last time term limits forced Russian leader Vladimir Putin to step down from the presidency, he became prime minister for a few years.

This time around, a group of pro-Kremlin activists have a different idea: Proclaim him Czar Vladimir.

“We will do everything possible to make sure Putin stays in power as long as possible,” Konstantin Malofeyev, a politically active businessman, said recently to thunderous applause from hundreds of Russian Orthodox priests and members of the country’s top political parties gathered at a conference outside Moscow. They were united by one cause—to return the monarchy to Russia.

While there are no plans to crown a new Emperor and Sovereign of All the Russias, as part of the royal title once went, the idea raises the possibility Mr. Putin could stay beyond the two-term limit the constitution allows.

The Kremlin has given little sign of who may succeed Mr. Putin when his six-year term ends in 2024, leaving many to speculate, sometimes wildly, about what’s next.