Heimerdinger should be a power armor user.
You can keep most of the abilities almost exactly the same. The grenade and rockets are both things someone wearing power armor could theoretically throw out.
The turrets would be re-worked so rather than being put on the ground, Heimerdinger attaches the turrets to himself. It increases his HP by a little bit, and they begin to do damage in an area around him passively. As Heimerdinger takes damage, the turrets would fall off, making him lose the max HP they granted while they were on. It would be basically be an ability form of Sunfire Cape.
The ultimate could be left roughly the same, upgrade all of the turrets on himself to do a little more damage and give a little more max HP, or it could be tossed and another suggestion from across the boards could be put in its place.
This would make Heimerdinger fit far better into the playstyle that this game has come to know, while only slightly changing how the turrets work. This would require a good amount of balancing to get all the numbers right, such as how fast he should be able to attach the turrets, as well as how much mana they should be, but the outcome I believe would be much more healthy to the game.
He would also require new art, but a yordle in power armor would be pretty badass.
Thoughts/comments/suggestions on this?