The 3DS is going to answer DSiWare fans' prayers (except for the one about not having to pay 300 bucks for a new system). A hardware fact sheet
(PDF) notes that it is possible to move downloaded software from one 3DS to a newly-purchased 3DS (at least, if our translation is accurate). In addition, it is possible to move downloaded DSiWare from a DSi or DSi XL.
Some (unspecified) software can't be moved, and Nintendo warns that there are limits on the number of times a transfer can be undertaken, but this is leaps and bounds ahead of the DSi's current limits, which are set at zero games and zero times.