Making a #5 is obviously largely dependent on the success and public reception of On Stranger Tides. Based on the first weekend, it seems to be off to a good start, although not as high as the first 3. I guess they'll have to see how it does long-term. I don't think Johnny Depp would oppose doing another, based on how it was basically because of him that they decided to do #4!
I personally love the Pirates series, and would be fine if they stopped, but would also always go see another if they chose to do one. If you ask me, Disney is open to continuing, because the plot was left wide open.