If the product is of high quality (which it will be), and priced fairly, I do not think you will need discounts to attract potential clients; it'll sell on it's own merits (and that will send the best message to competitors).
How do you determine if someone is a current license holder? What defines current?
I believe that if they're going to run with a sale, it should be open to everyone. After the sale ends everyone gets the same price. To much work would in my mind would go into trying to verify who owns a license, what does current mean, etc.
For example, today I have 10 vB licenses and 10 IPB licenses, I purchase 5 XF licenses, do I get a dicount only on my first purchase? Do I get a discount until i match the XF licenses? Do I always get a discount for having those third party licenses?
Bad Idea, they're 'most likely' going to have an 'early adopters' sale, doesnt matter if you're coming from vB, IPB, MyBB, PHPBB, SomeOtherBBwhichsucks - everyone should get the same price, and I say this as a license holder of 5 vB and 2 IPB, so yeah.
As a customer sure I'm fall all and any discounts... military... senior citizen... child... (not that I'm any of those) but realistically this has nothing to do with vBulletin.., Kier and Mike don't make any money from vBulletin sales so what logic is it they should give discounts to vBulletin customers any more than Microsoft or Apple customers?