There’s actually a much simpler way for Asana to sort this…
I too am struggling to choose Asana over JIRA due to the fact I require a short task ID which will be automatically incremental, use no duplicates, and can have a customisable format (such as 3 letters, a dash, and 6 numbers: ABC-123456).
The simplest way for Asana to provide this functionality would be to develop a new custom field type which could be made mandatory, allowing the functionality mentioned above. Then, people would have a simple ID to share with clients. The actual URL of the task would be in the same format as currently. So long as the short task ID were searchable in the standard search field, this would be really good.
Until this is developed by Asana (which hopefully won’t be long at all), JIRA’s out-of-the-box functionality with task IDs is the way to go.