Actually my GP has mentioned Gabapentin, but as I am already taking Pregabalin and Cocodamol (as well as my usual PD meds and other meds for other conditions), he decided to wait until we get the results of the MRI scan before he makes a decision re treatment.
Interestingly though, a couple of years ago I was suffering from really bad involuntary movements and I read somewhere that Gabapentin could be helpful for that. I mentioned this to my neurologist at my next appointment and he basically dismissed the idea, although he did admit that a lot of drugs, which are prescribed to treat one condition, turn out to have "beneficial" side-effects for other conditions.
I now take Topiramate for my involuntary movements. Like Gabapentin, Topiramate is a drug which is usually prescribed for epilepsy. But it has been found to have beneficial effects on PD too. And Pregabalin, which I am already taking for my sciatica, is another epilepsy drug! (which is also prescribed for neuropathic pain)
At the end of the day, I guess it's all linked to the brain!