You act as though Sherlock took a fucking holiday for two years. No way he was doing anything important. Is it not possible since you want to believe what Sherlock says so badly that John may have blabbered, if Sherlock had told him? Maybe John is a fucking blabber mouth who would have ruined his work taking down the web. Maybe John actually could not be trusted with that info. I think Sherlock would be able to accurately assess that.

Truthfully?

I doubt that was Sherlock’s real reason for not telling John.

Considering that John has successfully kept the secrets of lords and queens and the British Secret Service in his time with Sherlock, I really do find it unlikely that he would actually blab.  But honestly I think that Sherlock saw John mourning him at the grave, and thought, “I know what I’ll do, I’ll come back when I’m done and surprise him and impress the hell out of him by granting his seemingly impossible wish.  That’ll be awesome!”

And then two years later he turned up in a fancy restaurant and realized that he had vastly miscalculated. 

That really sounds more like Sherlock, doesn’t it?

But all I have to base that on is a thoughtful downcast look, a clueless conversation with Mycroft, and an expression of dawning horror when faced with John’s busted-up rage.  So, really it’s headcanon.

He was taking a holiday, though, in a Sherlock way.  I mean, most people would go to the beach.  Sherlock globe-trots and joyfully risks his life tangling with crazed Serbian crime lords.