That would just be a trade off for you being able to shoot it or its limited movement on the table, (like on a board with tightly packed scenery and such.)I wouldn't have any issue with it. It is larger and easier to hit. The only thing I can see that would be a problem is the range of psychic powers and leadership effects for embarked units, as they are measured from the vehicle.
I would not have an issue playing against it because it really isn't going to be too overpowering due to size or the weapons or the armor value. On the contrary, it might only make it harder for you to field effectively due to its size. I would think it would be an equal trade off as far as that is concerned.
For modeling the front ramp, I would consider using two regular raider ramp parts trimmed to fit between the tracks and generous amounts of plasticard to fill in the blanks. If you want it to actually open and close, (like a normal raider model) that will require some more engineering on your part, but I see it as feasible. I like the idea, I hope you go forward with it.