I second that concept -- the feature should be an option in X-Cart and it is not worth $50, especially if the feature has already been developed.
I mean, this isn't a full add-on module or anything!
Although, in my opinion, the feature should also have the option to insert the expected availability date and give the webmaster the option to take pre-release orders or not.
In a similar line, we should also have an option to set the status of a product to 'backorder' and be able to take customer orders for the product even when stock is showing zero. An extra notification to the customer is all that is required to let them know when stock is expected.
And a third option, for those who handle drop shipped goods where keeping track of stock levels makes absolutely no sense whatsoever, perhaps a setting in the product table to make stock levels irrelevant?
Perhaps the X-Cart developers will want to take care of their customers' needs and develop these features for the next release?
Go X-Cart developers! Yeah!! (Just a little cheering to get the ball rolling.)