General Motors (GM -0.10%) said last week that its president, Dan Ammann, will soon leave that post to become CEO of GM's self-driving subsidiary, Cruise Automation. The move will be effective Jan. 1, 2019. 

It was somewhat overlooked amid the news of GM's restructuring, but for GM investors, this announcement has important implications. In fact, it may be more important, over the long run, than that restructuring effort. Here's what we know. 

Kan, Vogt, and Ammann are shown standing in front of a Cruise AV, a Chevrolet Bolt modified with self-driving hardware.

Cruise Automation co-founders (from left) Dan Kan and Kyle Vogt with GM president Dan Ammann. Ammann will become CEO of the GM self-driving subsidiary on January 1. Image source: General Motors. 

What's happening: Ammann to lead Cruise

GM said that Dan Ammann will join Cruise as CEO, taking over from co-founder Kyle Vogt. Vogt isn't leaving: He will continue to lead the development of Cruise's self-driving technology as its president and chief technology officer. (Cruise's other co-founder, Dan Kan, will remain in the role of chief operating officer.) 

Vogt has run Cruise since it was acquired by GM in early 2016. In that time, he has led the company's growth from 40 employees to more than 1,000, led the development of a mass-producible Level 4 self-driving vehicle, and attracted outside investments from SoftBank Group's (SFTBF -3.14%) Vision Fund and rival automaker Honda (HMC -0.57%). 

Vogt isn't being replaced because he hasn't done well. Ammann is taking over because the next phase of Cruise's growth is operational: With its self-driving car nearly ready for production, the company is gearing up to launch a self-driving taxi service. Ammann, who led GM's effort to acquire Cruise and has overseen the business since, has developed close relationships with Vogt and Kan. He's the natural choice to lead the company as it begins commercial deployment next year.

Is GM planning a Cruise spinoff? 

Is this another hint that GM might be preparing a spinoff of Cruise? 

Ammann's move wasn't entirely unexpected. GM seemed to hint at the possibility in June, when Ammann handed off responsibility for global product planning and the Cadillac brand to Mark Reuss, GM's product-development and purchasing chief. At the time, GM said Ammann would spend more time focused on Cruise. 

Why would GM consider a Cruise spinoff? The answer is simple: To unlock a higher valuation. Wall Street analysts have suggested that Cruise might deserve a significantly higher valuation than it receives as a GM subsidiary, because of its potential as an early mover into self-driving taxis. If GM found a way to create a separate stock for Cruise, allowing investors to take a direct stake in the upcoming self-driving taxi business, its value -- and the value of GM's stake -- could rise sharply. 

The addition of Ammann, who brings operational experience and is highly regarded on Wall Street, seems likely to support a hefty valuation for Cruise. 

The upshot: This could be a big win for GM investors

A Cruise spinoff would be great news for GM's current investors. While there's a solid investment case for GM as it is today, it's hard for growth-minded investors to get too excited about a century-old industrial company. 

However, if GM found a way to give investors direct access to Cruise's growth potential, without the baggage of GM's "legacy" business, I suspect it would draw a lot of interest. Stay tuned.