I think the Lynx is the radio of the future (with new updates), but it came out over a year ago- a long time to not offer a new product.
It depends on how you look at what SiriusXM is trying to accomplish. We needed devices that provided Xtra Channels and the EDGE and LYNX were released to do exactly that. Existing hardware couldn't access the extra encoding/spectrum technology. Whether Xtra channels are really worth anything, is a whole other situation.
SiriusXM is here to provide a subscription service. The hardware is just a means to access the service. If there were a technical reason to release new product, they'd do it, but I think the age of incremental hardware upgrades with minor changes is likely dead. It's expensive to develop and tool for a new product.