I think it is. Continuing the story where the 3rd left off seems pointless when you think about. The writers will have to come up with a whole new plot device to bring back all the dead transformers which for the most part has a huge potential for being lame. How many times are we going to resurrect these guys? A prequel will take us to the war on cybertron (something everyone's been wanting to see). It will also give us back our favorite transformers (jazz, ironhide, soundwave, starscream, megatron, etc). Not only will a prequel bring our beloved transformers back from the dead, but it will allow for cybertronian modes which equals new toys (to make hasbro happy). A prequel will also allow for a way to properly tie in the events of all three TF movies we already received - filling in some plot holes along the way. I think this is really the most logical direction for the franchise to go. Similar to the effect of starwars where lucas waited for advancements in technology before he filmed the first three movies, now that TF's has proven they make bank, the studio can dedicate more money to the franchise so we can have more cgi elements (like cybertron scenes).