The best possible answer to the question in the title is 'not very likely' if for no other reason than the rights to host the Cup have already been awarded to Brazil. For those unfamiliar with the process, host countries are selected by FIFA, the world governing body of the beautiful game, under a competitive bid system. Brazil was awarded the 2014 Cup in 2007. This lag between announcement and opening ceremonies, typically anywhere from 6 to 12 years, is built-in to provide the lead time during which the winners can make all of the upgrades to airports, hotels, infrastructure and stadia that they promise in their bids.
Given this information, the question in the title to this post would be silly indeed if it weren't for Brazil's clear lack of progress toward many of the goals it set out and agreed to as prerequisites for hosting the Cup. Those familiar with global sports will know that the completion (or not) of many of these infrastructure improvements will have an impact on the Summer Olympics in 2016 as well as the games are scheduled to be held in Rio.
One might ask why the Cup was granted to Brazil if the country was so unprepared. The answer has to do with FIFA and its policies, and the body has many reasons for awarding countries hosting rights to the World Cup. Within the loose parameters of its new continental rotation schedule, it looks to reward countries that have helped contribute to the growth and popularity of the game (i.e. Brazil), looks for areas of growth (think the U.S. in 1994, Qatar in about a dozen years), and often seeks to make societal statements (think of a post-segregation South Africa in 2010). And, of course, those familiar with FIFA will be well aware of the plain old politics that goes into decisions as well.
As a result of these efforts to use the World Cup to meet other goals, FIFA is looking to increasingly novel, even far-flung, places to hold the tournament. As the organizers' other big desire is ensuring that big dollars (euros, yuan, yen) make their way to see the most popular sporting event on the planet, things can get messy.
While Brazil is a traditional power and has actually hosted the World Cup before, the tournament has certainly grown in stature since 1950, and the country wasn't game-ready when it won its bid. Therefore, as noted above, FIFA got the hopeful hosts to agree to huge amounts of improvements to ensure that the big money will attend. Such improvements are not always easy or cheap to undertake; if they were, the country would have been working on some of them already. In sum, Brazil faces a conundrum as a growing country with less-than-perfect infrastructure which has been granted host-status, forcing its leadership to agree to improvements the nation may not be well-positioned to make.
Now, it would be worth noting that no one forces countries to make proposals. Particularly with all of the available information regarding the (lack of) economic benefit which can be derived from hosting large events, any nation offering its services as a host-nation for the World Cup (Olympics, etc.) is well aware of the slightly Faustian nature of the bargain it is potentially making.
However, as a practical matter, politicians, the national mood, and finances (especially in a commodity-export-dependent nation like Brazil) can change dramatically from pitch book delivery day to the day of the final. While Brazil's leadership won't say so on camera (especially since the tournament is so popular with voters), it appears as if its mood on the World Cup has soured a bit. Some of the pols who had pushed the proposal through are no longer in power, and there is less appreciation of host status at the top currently. This has led to lack of urgency. Along with an always ambitious implementation schedule, this has led to a situation where only 5% of necessary projects are ready with only two years to go. This state of affairs is why the answer 'not likely', can't be just plain 'no'.
The U.S. is widely seen as the standing replacement for Brazil if one needs to be found in short order. There are international-ready stadia across the country, a robust hospitality industry, and politics which all make the U.S. the natural, easy choice. For those unfamiliar with recent events, the political reason stems from what many insiders perceived was a slight against the country during the latest selection processes when Russia and Qatar were selected over the U.S. in minor and major upsets, respectively. In short, the country would be willing and able to put together a World Cup on short notice and do it well, all while serving at least one political goal (a non-apology apology) for FIFA.
However, despite the convenience that would be for yours truly, it would be a shame. Brazil is a huge footballing nation, and it would be nice for its fans to have a taste of the world's biggest tournament on their home turf. Although that goal is slipping away, if only slightly, here's hoping that efforts are improved before that slight slip turns into an unstoppable wave.