I agree, maybe there will be a power armor mod that will turn that walking tank into a more... hulking version. Let's just say it only makes it bulkier and a bit taller (not making them as big as the FO4 behemoths though), and instead of using handheld weapons as its armament, it would use arm-mounted weapons that are the more heavily armed version of some handheld weapons e.g. chaingun for minigun, plasma caster for plasma weapons, laser cannons for laser weapons, pneumatic hammer/ arm-mounted sawblade for melee weapons

The modification might turn the already-durable and formidable walking tank into basically... A dreadnought of death and destruction. The downsides might be that normal power armor attachments could not be used, it is considerably more slower, and it eats a lot more energy than normal power armors... (Even with fusion generators) And oh, because they are bigger, they are a lot more less maneuverable and could not pass through some spaces... That would be considerable downsides which might more or less be balancing and making the option less attractive, also considering that we could now attach jet-packs to power armor, which is very cool and make the normal power armor more advantageous in more situations.

That could be a reward for siding with the Institute, given that they are researchers who are capable of creating advanced techs such as androids... Creating a prototype heavy power armor might not be that far off for them. Also, that vertibird that the player could use might be the reward from siding with the BoS... (and other rewards obviously, such as calling in a BoS squad, maybe?)

Exactly! I think people heard the word "mech" and thought of a metal gear or one of the mechs from Armored Core. I just meant something bigger and bulkier than power armor, but WAY less over the top than Liberty Prime. So it would be too big to fit indoors, but not big enough to ROFLstomp a building.

Unless there are enemies of equal or greater strength to something bigger, like a mech, and in enough quantity to justify something bigger, I personally doubt there will be such a thing.

I do, however suspect there's room for variants, like a light, and heavy power armor where we see the heavy version(s) in the trailer, and E3 videos.

From the concept art teased before the game play sections of video, there certainly seems to be a variety of faction style armors, like an alien(?), and certainly others that are faction related.

I'm a little curious about what stealth armors will be available, and how those might be implemented, but, that's another subject.