Short answer - they've said nothing.
Very true. I also would like to see the upgrade offered.
While I have no quarrel with the "no announcement of pending upgrades", I admit to being curious as to why the delay. Is something in the 436/536 design prohibitive of enabling NXDN? The other possibility I have wondered about is if Uniden has not been able to negotiate a rights/royalty agreement on the feature.
Whistler has focused DMR & NXDN upgrades on receiving the related emission codes, not in actually trunk tracking the systems. For the low to medium activity systems I monitor, it works reasonably well. For both DMR & ProVoice, UPMan has indicated that they are paying royalties for each upgraded scanner. That, plus I would presume development cost, are parts of the reasons for the paid upgrades. If they are unable to reach a similar agreement on the NXDN trunking IP, then that may preclude the option being added. I would hope, if that is the case, Uniden would fall back to an emissions code format similar to Whistler's.