This theory is proposed by Rabbi Dovid Fohrman in his book, The Exodus You Almost Passed Over.
Rabbi Fohrman spends fully the first third of the book developing just questions on the story. In addressing these questions, he proposes that ultimately, Hashem's goal was not just to free the Jews, but to convince not just any nation, but the one most stooped in paganism, that He is the one true G-d, Who wants a connection with His creations. Egypt was the perfect candidate, as not only did they worship a pantheon, they were a powerful and stable society, one which viewed their king as their creator. What greater testimony to Hashem than to convince such a king that he, in fact, is not the true G-d?
Paroh enslaves the Jews because he can. He has the power to do so, and might makes right. Ultimately, this is the general philosophy behind paganism. By tearing down this philosophy, the Jews will go free automatically; these goals are two sides of the same coin.
Plan A was to give Paroh a nonviolent demonstration of Hashem's authority. Moshe provides some signs, with the hope that Paroh would recognize Hashem. The idea was that they would go for a three day journey, receive the Torah, go back, and teach the Egyptians about their newfound religion, all in incremental steps. Moshe first says that Hashem wants His people to celebrate with him, but Paroh isn't ready to accept this: "Who is Hashem that I should listen to Him?!"
Moshe then backtracks: Okay, you don't get a Hashem Who wants a connection. Certainly you understand serving a higher power in general, right? Paroh doesn't reject this out of hand; he simply says that the slaves are lazy, that they don't fear him as much as they do Hashem. So he ups their workload. But had he been willing to accept that at face value, they would have gone out for their three day celebration, received the Torah, returned, and continued teaching the Egyptians, in incremental steps, what it is that Hashem wants of them.
Take a closer look at the story surrounding Yaakov's burial. There's a lot of details which parallel Yetzias Mitzraim: the archers, the route taken, the deliberations about the kids and cattle, etc. Perhaps this was supposed to portend what should have happened later on: The Jews would go out for their three-day celebration, receive the Torah, come back, teach the Egyptians, and they'd all go up to Eretz Yisrael together as Hashem's people – and other nations would join in, too, as they did in Yaakov's burial.
Instead, Paroh declares war, and so Hashem declares war in return. A polytheistic god will display power, but not precision; a monotheistic G-d is capable of both. Throughout the plagues, a careful reading will indicate that Paroh is testing Hashem's precision: he wants the frogs gone tomorrow, rather than immediately; he notes by the Arov and Dever that they didn't affect the Jews, only the Egyptians; and so on.
But Paroh can be stubborn, and so a Plan C must be devised. Barad is the deciding factor whether Plan B or C will be the successful one: Barad is somehow tantamount to all the plagues combined; that it's only for this that Hashem has kept Paroh alive; that Hashem warns Paroh of how to avoid its destruction, as a monotheistic G-d Who cares about His creations rather than a polytheistic one who just displays power; that fire and ice are combined into one, something absolutely impossible in a polytheistic worldview. Paroh finally admits that Hashem is in control, but simply doesn't care; that's why only at this point does the passuk describe his stubbornness as a sin. He's too proud and arrogant to let the Jews go at this point.
Plan C addresses this possibility: if the Egyptians aren't going to be actors in Hashem's display of authority, then they'll be His pawns. No longer is it that Egypt will know that Hashem is the true G-d, but that you, the Jewish people will know. The Egyptians are no longer actors, but rather pawns, in Hashem's revealing to the world His authority. Paroh's servants get it: "Until when will this be a trap for us? Don't you know that Egypt is lost?" They see that Paroh is being trapped in his arrogance, and that Hashem is the one in charge.
Because Plan C is playing on Paroh's arrogance, while Paroh keeps requesting that Moshe let him save face, Moshe's not having it. They're going to be taking everyone, and all of their animals. No deals are going to be brokered here. And as Paroh gets more desperate, Moshe intentionally provokes him: not only are we not leaving any cattle, why don't we take some of yours, too?
Leading to the climax of Plan C, the firstborn motif which is so prominent through the story – right from the beginning, Hashem says that Bnei Yisrael are His firstborn, and so the Egyptians' firstborn will be killed as a result – comes full circle. Those who are willing to be Hashem's firstborn, to have that connection with him: they can survive. Those who are only firstborn of a human will perish.
Finally, Kri'as Yam Suf. If you read carefully, it's basically a repeat of Creation all over again: there's the wind blowing over the waters, the separation of light and dark in the form of the pillars of cloud and fire, the separation of waters, the drying of the seabed. Chazal are winking at us when they propose that there were fruit trees growing in the Yam Suf, as if to reassure us that this pattern is real: after all, vegetation was the next thing in the Creation story after the drying of the continents. The irony here is perfect: in this momentous display of Hashem's having created the world, the Egyptians, who refused to serve their Creator, drowned in the sea, as these signs of creation were removed and the waters crashed down on their head. You want to deny a world with a Creator? Then live in a world without one.
Your suggestion that "the original intention was for the Jews to go out of Egypt to receive the Torah, and then come back to convert the Egyptians." was indeed the Plan A. Paroh wasn't up to the task, so Plans B and C had to come into play, to ultimately show them, the Jews, and the world that "there is none like Hashem in all the land."
I've attempted to pose his basic theory, but I can't possibly do it full justice. There's so much more than what I've described here. I highly recommend that you take a look at his book if you're interested in pursuing this further.