I don't really see the point in a remake, but I wouldn't be averse to a sequel, provided that they stick to the following restrictions:
* No more 'glitch' memories of Murphy's wife and son. By the third movie, that got a little stale. They're gone, time to move on.
* No more crazy-a$$ upper-level thugs in cahoots with OCP. Even that nutty REHAB chief was just that - a thug.
* No more resorting to inept killer robots to do away with Murphy. Keep the ED-209s around for macabre comedic moments, though.
* No more Detroit police strikes. OCP will always treat the cops like sh** as long as OCP exists. They should know that by now.
Most importantly -
* Do something to the suit that will get Weller back. Heck, if his sensors are as powerful as they should be, Murphy wouldn't even have to move fast at all, even if he had an upgraded body; that would allow for a more maneuverable suit. He wouldn't have to be fast, but it could be more measured, precise movement.