This will work for well known words, the problem with this method is that there are many four letter combinations that are not necessarily English words but will be contractions of words or acronyms: MUFC => 'Manchester United Football Club', PLNE => 'plane'. There is also L33T which bends the rules by using numbers. Just call 0800 123-SK8R for your local half pipe...
You are right, I mainly presented this as an easy hack of getting 90% there. Even with the examples you give, if I have my own dictionary, or generate a special one ahead of time, this procedure will work fairly well. For example I can generate abbreviations, without too much effort, from an existing dictionary which will cover your PLNE example. (L33T requires some work, but if you use it I pity you.) The dictionary your method uses is in a human's head. Sometimes these work well, sometimes they don't.
Re: MUFC -- I'll probably get downvoted/flamed for this, but I'm a reds fan. To some that is truly a 4-letter word. :-)