In short: No.
This is a reboot, not a remake. They are two very different things.
In a reboot, ALL previous content is ignored for the purpose of beginning a new franchise. Bringing back Dr. Serizawa alone is something of a risky and bold move on the part of Legendary as it breaks pattern for what it means to create a reboot. However, having the good doctor back for the sake of nostalgia is acceptable, though he is not going to be the same as he was before obviously. There won't be an oxygen destroyer this time around, nor does he have his eye patch (for all those Serizawa buffs out there).
Bringing back Toho monsters (even mechanical ones) is not something Legendary should do, nor is it likely that it will happen at all. Acquiring the rights to all of the different creatures is crazy expensive and not worth doing. We all love Toho monsters, but bringing them to the big screen in an AMERICAN franchise run by Legendary Pictures is not something that should happen. They are Toho monsters, and they are meant to be used by Toho. They are on board the project to make sure it goes well and that Legendary doesn't stray from Godzilla's design. They are not actually in charge of what happens, nor are they actually technically affiliated with the Legendary franchise outside of owning the original Godzilla character.
Toho has no input on what Legendary's story is, the human characters, nor anything else involved save for Godzilla himself. Toho is not going to give Legendary their monsetrs just to please a few fans that want to see them on the big screen in CG as opposed to a 1960's or 70's suit. Contrary to popular belief, big name companies do NOT always appease the fans, nor do they even pay attention to them most of the time. They pay more attention to professional criticism and total income than they do fan reaction.
Your idea might be interesting for a fan comic, if you'd care to write it on a public online fan fiction writing website, but as far as being a possibility for a movie produced by Legendary, not happening.
