There are so many problems though that would come with a mobile suit.
1) Cost... to build something like that, and to mass produce them would be expensive, and it would probably take years to develop a working machine.
2) Moving parts... a huge problem with even our fighter jets. The Mobile Suit would be so clanky and odd that it would hardly be maneuverable on a terrain surface. Not to mention with so many moving parts, it would constantly need repair, which would up the cost even more.
3) Power, it would have to have an external power source, because it would be way to hard to run this thing on fossil fuels, in fact I'm sure it wouldn't even be powerful enough.
And even if we did develop a more lightweight armor material, it would most likely be given to the tanks. Besides, what is the need for such a weapon when we can do military operations without our enemy ever seeing us? I think the future of our military, at this point, is working on ways to create GPS based weapons and satellite based weapons. We will see more accurate missiles, and things of that such long before we ever see a mech. The closest thing to a mech I can see is a armor suit.
Also, robot technology isn't advanced enough. To create the computer system in this machine would probably take longer than the machine itself.
How all of this is combated in Gundam... well..
For cost, Asteroids where brought in to surrounding areas, and mined, also... they discovered new forms of existing metals, and where able to purify them more to create Lunar Titanium (Later Gundanium) Which was only used on high level machines (Like V Project mobile suits) because it was more expensive.
Moving Parts:
Since they are far enough into the future where people can successfully thrive in earth, it's easy to see that technology is far more ahead of our on in their world. Also, the use of a space machine creates less stress on mechanical parts, but I'm sure they had a lot of trouble with this issue.
And as for the power issue, that is already discussed in my small excerpt of Minovsky Physics.
So in conclusion... I think a mobile suit would be incredibly useless in our world, it would be slow, have to work on flat ground, and would easily get picked off by a missile or artillery shell. I doubt we wont see anything like that in our lifetime, or our children's lifetime.