What is Elon Musk's secret masterplan?

The Tesla boss has been teasing Twitter...

SpaceX, Elon Musk, business

Jae C. Hong / AP

He's been coming in for some criticism of late having announced Tesla's intention to merge with his own SolarCity, while Tesla has had to deal with its first reported self-driving car fatality but Elon Musk still has his eyes on the masterplan.

More specifically, the masterplan part two.

The Tesla founder took to Twitter last night – on the legendary Nikola Tesla's birthday, no less – to give a vague update on his business, with the suggestion that more would follow in the coming days:

The term relates to the original "Top Secret Tesla Masterplan" he outlined (publicly on his blog, of course) almost a decade ago.

It read, in short:

Build sports car

Use that money to build an affordable car

Use that money to build an even more affordable car

While doing above, also provide zero emission electric power generation options

Don't tell anyone.

With that plan becoming a reality as the car company gets ready to roll out its Model 3 sedan in 2017, social media has been hazarding guesses at what the Bel Air-based entrepreneur and inventor has up his sleeve this time.

Musk's own Twitter activity played into suggestions it will have to do with that acquisition of solar panel provider SolarCity.

He said of an article suggesting that reducing the cost of making a house-powering battery so every Solar City installation can be both a power plant and a storage system:

And the closest guess yet, according to Musk?