President Putin's shake-up seems to pave the way for him to stay in power as PM in 2024

It's not clear whether Dmitry Medvedev's resignation as prime minister came as a shock or whether it was all part of President Vladimir Putin's plan.

Perhaps it doesn't matter.

Mr Putin now has the opportunity to cherry pick the next prime minister and other key cabinet posts as he chooses.

He's just appointed Mikhail Mishustin, chairman of the federal tax service, as prime minister, and given Dmitry Medvedev a newly-created role as deputy chairman of the security council, not exactly a promotion by the sounds of things.

So what next?

In his state of the nation address today, the president outlined an array of possible constitutional reforms which would broadly realign the balance of power in Russia.

Now follows a consultation period and a possible national referendum but essentially, he's diluting the power of the presidency and strengthening that of parliament and the prime minister.

It will be the parliament who will appoint the prime minister, not the president, though the president will continue to make security and defence appointments.

The million dollar question for anyone with even the faintest interest in Russia is what happens in 2024 when Vladimir Putin is constitutionally obliged to step down.

He will have been in power for 20 years by then; 24 if you count President Medvedev's four-year term where Mr Putin held the post of prime minister.

Mr Medvedev is a spent political force.

He's unpopular with the public and appears to have exhausted the president's patience.

Any repeat of that Putin-Medvedev job swap is likely off the table.

But today's proposals seem to pave the way for Mr Putin to return to the role of a prime minister, one imbued with far greater constitutional powers than now.

Another option is that he could head up a beefed-up state council, a relic from imperial days he's talking about reviving and giving constitutional form.

True to form, Mr Putin is keeping it vague.

But for all the talk of parliamentary consultation and putting the question of constitutional change to the people, it's quite clear who's pulling the strings.