Errr, there will be a tradeup incentive. MkI owners will get a discount on the new model - it's not fixed yet how much, but it will be preferential both in terms of when you get the unit and pricing.
As we've said, we're not leaving MkI's unsupported, as the MkII has almost everything in common. The only thing we're not doing is taking MkI's back in part-exchange: it's easier for you to sell them to drooling friends than it is for us to have a large number of units back here :)
Not wanting to labour the point, but as Rob said it will be 3-4 months from when the last MkI ships to when the MkII ships. Your unit is still exactly what you originally paid for, and most other companies (Apple, etc) wouldn't give you any discount on a new model even if you bought it the day before the new model came out: things move on. Either we keep up or fall behind - I'm sure you'd prefer us to keep up.
Hugo