It would be nice to have:

- different products upsell to different subscriptions

- ability to add a "free" product as an upsell. At the moment we are forced to put in a price - what if we want to offer a free gift with subscriptions but don't want to force it on every customer?

- flexible price on the upsell product based on the subscription tier or trial price the customer is paying. E.g. if cart total => $x, then upsell product price is $y.