Kremlin's worst nightmare

The details still need to be decided, but the revolutionaries have won in Ukraine. Some elements of the old regime may survive, but that is precisely why the protesters on the “Maidan” (Kiev's main square) don't trust the mainstream politicians who claim to be negotiating on their behalf.
The politicians in suits can write a new constitution to improve on the old one they have just restored and try to save the collapsing economy, but the Maidan leaders in the fatigues and helmets will set the agenda on justice – dismantling the militia and reworking the corrupt legal system, so that the many guilty end up behind bars.
All of which is the Kremlin's worst nightmare. When the protests started back in November they were about a trade deal with the EU. Russia was ecstatic that it had persuaded Ukraine to walk away from that deal, and was picking off the other states in the EU's “Eastern Partnership” programme (Armenia caved in September, Georgia and Moldova were  expected to come under enormous pressure in 2014).
But this is 10 times worse than Brussels expanding its bureaucracy to Russia's borders. A real democracy in Ukraine is an existential threat to the entire system that Vladimir Putin has built since 2000. Ironically because Putin is right – most Russians regard Ukraine as a kin state, or not really a different state at all. They are used to stepping in tandem; so if something changes in Ukraine, why not in Russia too? Other Maidans might appear in other neighbouring states – maybe first in Moldova where the Russia-backed Communist Party was hoping to return to power in elections due in November.
The new government in Ukraine, however it's made up, will be given the briefest of ritualistic honeymoons before Russia uses every instrument at its disposal to try to make it fail. Unfortunately, Russia holds most of the economic cards.
Russia's “soft power” isn't particularly soft. The new Ukraine will pay more for gas, which will be regularly cut off for “technical reasons”. Russia's “food safety” agency will declare that everything that comes out of Ukraine is radioactive. Ukrainian migrant workers will be sent home now they have finished helping to rebuild Sochi.
Worst of all, Russia will work hard to try to re-corrupt the political system. The Kremlin used to boast that it could exploit Ukraine's old-style “democracy” – meaning that, just like Yanukovych, they could launch their own puppet parties and buy agents of influence in the honest ones.
But Russia's ultimate problem is the same as Yanukovych faced. The Kremlin simply can't understand that protesters would be motivated by ideology rather than by money or foreign support. The Russians were good at manipulating the old system, but dealing with real revolutionaries is a different matter. Ukraine is starting a very bumpy ride.