I've been critical of SodaStream (SODA) for quite some time. Last June, when the stock was trading near its all-time high, I pointed out that the company had an absurd business model based on a fad -- for the vast majority of American consumers, brewing their own soda just didn't make any sense.

I might have been wrong about the business model, but not about SodaStream. Already battered, SodaStream is poised to get crushed: unless it does a deal with PepsiCo (PEP -2.97%), Green Mountain Coffee Roasters (GMCR.DL) and Coca-Cola (KO 0.15%) will conquer the market.

SodaStream is already on the ropes
SodaStream shares are already down more than 50% since last June. A string of disappointing earnings results have hit shareholders hard -- in January alone, shares lost about one-fifth of their value after SodaStream gave disappointing guidance.

For fiscal year 2013, SodaStream expects to post net income of $52.5 million on revenue of $562 million. That's up from 2012, but not by much -- if SodaStream's estimates prove accurate, revenue will have grown about 29% in 2013 while adjusted net income rises just 5%. In contrast, both revenue and adjusted net income were up more than 50% in 2012.

In other words, SodaStream's growth is slowing significantly, casting doubt on the company's long-term prospects.

A challenger approaches
To make matters worse, SodaStream is about to face its biggest challenge yet. Sometime next year, Green Mountain Coffee will launch its "Keurig Cold" -- a new brewing platform centered around carbonated and cold beverages. Green Mountain hopes to replicate the success it had with hot beverages in the cold beverage space.

Longtime Green Mountain observers will know that its growth over the last half-decade has been a story of partnerships -- slowly but surely, Green Mountain was able to ink deals with most of the big coffee makers, adding new varieties of K-Cups and strengthening its platform over time.

SodaStream has been attempting something similar, working to bolster its line of off-brand drinks with name-brand products from major companies. But when Green Mountain comes to market, it will be with the biggest of partners. Both in the U.S. and globally, Coca-Cola dominates the cold beverage space, with legendary brands like Coca-Cola Classic, Diet Coke, and Sprite, not to mention its portfolio of products in other categories like Powerade, Minute Maid, and Full Throttle.

Is there any hope for SodaStream?
Wednesday's news was a major blow to the SodaStream story, but shares are rallying on Thursday anyway. Investors seem to be pinning their hopes on a deal with PepsiCo -- if Coca-Cola wants in the business, shouldn't Pepsi follow suit?

It's possible that SodaStream could do a deal with Pepsi, but betting on such an outcome seems inordinately risky. There's no guarantee that Pepsi will mimic Coke's move, and even if it does, it could develop its own competing system, or partner with another company already in the space (Hamilton Beach, Cuisinart).

If Pepsi does partner with SodaStream, it will be a boon to shareholders, but if not -- watch out. When Green Mountain enters the market next year, it will have the support of Coca-Cola, a major advantage.

Prospective consumers trying to decide between the two machines will have the choice of going with SodaStream, and its line of off-brand cola, or buying Green Mountain's solution, and being able to brew Coke, Diet Coke, and Sprite in their homes. The choice seems overwhelmingly obvious.

Barring an acquisition from PepsiCo, or a similar deal, it's difficult to see how SodaStream stays relevant in the face of what's likely to be an overwhelming competitor.

Editor's note: A previous version of this article stated that SodaStream had made a deal with Dr Pepper Snapple in the past. The Fool regrets the error.