I don't think this is the last we saw of him

To explain this comment: Borisov isn't a standard centre-right leader, but a populist. Populist not in the US sense, but a sense as commonly applied to a type of politics widespread in the ex-communist region, characterised by the championing of a selection of hot-button popular demands whatever the consequences, a fake anti-establishment attitude (perhaps the key feature), one-man parties, and ad-hoc decisions. Few of these populists rise to the top, but when they do, it's in places where the establishment really did itself in: the prime examples are Italy's undead several-times-PM Silvio Berlusconi, Romania's President Traian Băsescu, Slovakia's PM Robert Fico, and Bulgaria's now-ex-PM Boyko Borisov. It is par for the course for such a populist to toss underlings and allie aside and pretend that all of the problems associated with a government are the fault of everyone else, the way Borisov did today.

_{*Lunatic*, n.
One whose delusions are out of fashion.}

Is July the earliest that elections could be held? Seems like a long time in a ministerial parliamentary type of government.

"It is not necessary to have hope in order to persevere."

There is now a long analysis at Novonite: Bulgaria: The Bulgarian Winter: Between the Devil and the Deep Blue Sea. It details both the political manoeuvres preceding the government's resignation (including an attempt by Borisov to stop the protests with the help of fake protest leaders!) and the politico-economic situation that led to the various protest movements. Of these, the grain producers' one might be even more significant (the yuppie ex-World-Bank finance minister tried to renege on a promise to them a week earlier, leading to his dismissal). But here is the part on the energy issue:

...while not all demands went against privatization and for protection, this was the overall frame: a frame that has proved difficult to articulate after decades of a systematic liberal pro-market brain-wash.

The latest wave of contention that led to the resignation of the cabinet made no exception, but by early this week, the demands had started to change. The initial demand for the decrease of energy bills gradually changed with the slogan "Let's burn the monopolies". This motto expressed the explanations of the government as to why the increase of prices had happened were various. The reasons given ranged from the tax on green energy, the slightly longer period of charging, the delay of the process of reporting and increased consumption due to the Christmas holidays, and the low voltage of the electricity for domestic consumption. These were all valid reasons, and it was not transparency that was missing in the price formation. The solution offered, however, by liberal intellectuals, the media, and also initially by the people in the streets, was - surprise, surprise - the end of monopolies and further privatization and liberalization of the energy market. Yet the whole process is a showcase of how privatized entities function out of state control. The power distributive companies were privatized in 2005 and then sold out to three foreign companies under very favorable conditions of secure 16% annual profit or return for them. This made the state - and thus the taxpayers - literally indebted to these private companies, which have on top of that held prices high with a cartel agreement. Yet, it was not the monopoly in general that was a problem: an issue which was eclipsed by the amnesia of 23 years of transition to market economy. It was the monopoly in the hands of uncontrolled and uncontrollable private companies within a free market economy with no state regulation or protection that made the population vulnerable to price hikes. Yet, the crisis of political representation seemed stronger and soon took a lead among the protesters. The concrete plea of concessions on the electricity bills were soon followed by an overall demand for the resignation of the government, which in some places took the form of claims against particular local mayors and representatives of the state. By Monday the demands changed more dramatically to a new Constitutional Assembly, majority vote with no parties but individual candidates, and the revision of all privatization deals and concessions for the last 20 years. Thus, while general discontent with the capitalist system only surfaced timidly in some of the protesters' demands, the crisis has become political.

...but before we go all optimistic, there are shades of Budapest 2006-7:

...The protests were also joined and partly hijacked by a number of right-extreme groups. Mobilized around the neo-Nazi march this Saturday, commemorating interwar General Hristo Lukov, the Hitlerite leader of the Bulgarian Legions, who and introduced anti-Semitic laws, they were ready to provoke and loot. Their reactions jeopardized the energy of the protests which peaked on Sunday, and resurged on Tuesday...

...A few parties in the extreme right, such as Ataka and VMRO, have tried to ride the wave of the protests. And while their thugs discredited the protests, their leaders have kept firm ground, calling for nationalization of the power distributive companies, and the resignation of the government.

_{*Lunatic*, n.
One whose delusions are out of fashion.}

Hardly surprising... In my view there has been consistent underreporting and misrepresentation in the anglophone media (can't comment on the other major languages) of anti-austerity protests in general. It is a kind of informal diffused censorship.

Resigning in order to be able to run as opposition (with the same program + make over) sounds like it fits.

Sweden's finest (and perhaps only) collaborative, leftist e-newspaper Synapze.se

Sure it's fishy... I suspect it is a move of the establishment to trick and deflect the protest. Practically all political entities in Bulgaria that matter espouse some kind of right wing politics notwithstanding what's written on the tin; and all of them have essentially the same paymasters. On top of that, all important economic and political decisions are not taken in Sofia, but in Brussels/Berlin and under the heavy american influence. When this context is taken in consideration I very much doubt the protests would lead to any meaningful changes.