Unless your just thinking of putting a gyroscope and legs on a truck or something. I dont see how that would be so hard.
Putting the legs on a truck isn't hard, but getting the legs to work ina reliable and usefull way is 
People can make working legs, getting the power to run them seems to be the problem.
Not even that - even the most advanced humanoid robots can't run very well, and none can walk far on anything other than flat ground. You can't guarentee any battlefield is going to be perfectly smooth.
I think the most likely development will be "drone" tanks, which could be controlled remotely. They already use drone aircraft, and there's no reason why one person couldn't remotely control a drone tank. A drone tank would have the same amount of weak spots as a normal tank - few - and has the added advantage of not putting its occupants at risk from the dreaded anti tank rounds. They could also be smaller and lighter, and possibly faster.
They are also making bomb disposal bots, to keep bomb disposal experts out of harms way. Most are reluctant to use robots as killing machines though - although drones are already doing just that.