I have been a member for a number of years and as such have purchased a lot of different products.
Sometimes I will see a product and purchase it but it may be a while until I get round to using it.
What this means is that despite not using the plugin/theme etc the support licence is still running down from the date of purchase.
This can mean that when you decide to try out the product the support licence is no longer valid as it has run out.
So you are trying out a product for the first time and find an issue that you may need help with but there is no support available because of the above reason.
If I am unable to resolve the issue myself due to the lack of available support then I will usually not waste time further on it and thus there is no encouragement to buy other items.
A fairer licence system
What if instead the support licence that is part of the purchase of the product purchased did not start to countdown in time until the first contact for support which would trigger that countdown.
That way you could make the purchase when you see the product and know that you would be able to get support when you got around to using the product for the first time where it is most likely that the need for support would crop up.
It is a fairer system for both customer and seller in that the seller makes a sale and the customer gets to use your product at their convenience knowing that if they needed support it would be available.
This is not a request for an extended support licence for the product you are selling but timing of when the licence time limit is implemented.