Next you also have liability issues to deal with. Ever read the warning labels on a product or its instructions? The slightest problem with your radio link that causes an out of control mower to cause damage or injury. Well let's just say that you could loose so much that YOU will be mowing your neighbors lawn instead to earn a living after the lawyers suck your bank account dry.
Finally as I also say in regards to Engineering, "Just because you can doesn't mean you should". To illustrate this consider that I can build a combination cell phone and blender. Yes it will mix drinks and make calls but the features of one function negatively impact the feature of the other. Its a silly example I know but relevant to the design of any product. The features you add should bring more value to the product than they cost (in terms of impact and not necessarily money). The remote lawnmower may be easier to operate but it becomes harder to use (guiding the mower). Than what value have you added?