The whole project is dragged on by exorbitant back end deals for Bruckheimer, Depp and Verbinski. Then, you have the lack of licensing opportunity for merch. And of course, do people really want to see Westerns? Americans seem lukewarm to the genre these days, and I'm sure foreign countries are even less interested.
The first movie would literally have to be more successful than the first Pirates of the Carribean for this to make any sense. The first PotC grossed about $650 million, and yeah with lower tix prices and no 3D surcharges. But even based on the same # of tix sold, I'd say that the Lone Ranger would have to gross $850-900 million AT LEAST for this to be a viable franchise, since there's no point in doing a one-off.
If the first Lone Ranger grosses "only" like $550-600 million, will they continue making sequels? Even with a $200 million domestic and $400 worldwide, that barely cuts it, and I think both numbers would set records for a Western. If you stick by the rule of thumb that a sequel is justified only if the first film has enough of a net profit to cover the budget for the sequel, then you'd need at least $550-600 million ($250 budget for 1st, $300 budget for sequel). Even trimming down the budget to $200 would still require $500 worldwide at the very least.