If you want that, ask for a credit if you buy a new receiver from a retailer, like solid signal or others. That way you know you will get a HR24. I've asked for that and been granted a $200 credit in the past. If they just enter an order to swap it you may get another HR20.
They do not have a program to swap HR20s at this point. HR20s are 'current'.
If you have any interest in the HR34, you may want to hold off on that and see what they do come mid-Feb.
H20 cannot support the new HD interface, that would be the ticket for replacement.