It will be Transformers: Something of the Something yet again. Just like Star Wars 7 will be Something of the Something.
Also, it's gotta be engrish. Return of the Megatron, Revenge of the Decepticon, Cool of the Explosion, something like that.
=P In a nutshell. Mike Bay, he makes money based off of his goofy movies. Hasbro? Isn't exactly going to argue with money gain. Mike Bay "decides" to name it Trans4mers: Rise of the Mountain Robots. Hasbro isn't exactly going to argue with it. Why? Money.
Hasbro owns the brand. Hasbro has marketing concerns to deal with. The brand goes far beyond the movies.
That is very true, however it would be branding changing at all. Only the title of the movie. Hasbro could very easily call the movie title Trans4mers and then have the toys packaged as Transformers : Rise of the fall of the cat-zombies.
I would imagine "Trans4mers" will likely end up as the unofficial, colloquial, title that will be used by fans, the entertainment media and maybe even in some marketing materials...but there's no way it'll be the actual title. As others have stated, if the pattern of the previous movies continues, it'll likely be "[Something] of the [Noun]".
It seems like Hasbro likes to come up with something to break up the first part of a movie line with the second half of a movie line. So with the first movie you had Transformers and then Transformers Allspark Power. You had the Revenge of the Fallen line then Hunt for the Decepticons. Would not surprise me if Hasbro doesn't break up the next film's toy line into two different sub-brands if retail demand is strong for the figures.
M3gatr0n: OMG, 0pt1mvz Pr1m, I haz akqu1r3d n3w SOOPER WEPOOON dat w111 d3stroy teh Earf 0nc3 and 4 all! 0pt1mvz Pr1m: Fukk dat sh1t, M3gatr0n, 1'ma kicc ur azz str8 2 da m0000n! M3gatr0n: OMFG GTFO HAXXORNOOB! Add in a sunset, some potty humor, mixed in with some hot babes bending over sports cars, military KABOOMs, and the result will make over a trillion dollars and garner an infinite amount of fanrage
It would be downright hilarious if it was literally called "Something of the Something." Sadly, I'd still go see it.