The team just released the T7 and there are currently some users that are experiencing some issues with it and some of the staff is devoting their time to resolving those issues as they should be.
PMDG has a pretty fantastic track record of delivering on their promises in spectacular fashion, even if it isn't as timely as some would like it to be.
What gets old around here is the 30 posts a day of people asking what about this aircraft now? When will it be done?
Development of products, and testing of said products takes years and for good reason. It seems that each time PMDG releases a new product that they find a way to raise the bar on the quality and overall depth of the simulation for users. The NGX blew people's minds and the T7 has done it over again.
They could go ahead and just modify the NGX into the 739ER model and release it without adding any new features and maybe some of you would be happy, but many others would not be pleased with it not having some of the new features that are in the T7. All that coding to put in those new features and modify them for the airframe takes time and then more time for testing before it's released. (It's also worth mentioning that the ER is just barely being delivered to the real airlines and knowing PMDG they'd like to have some performance data on the ER before working on it.)
PMDG doesn't announce when projects will be done until they're ready to make an announcement, so what's the point of asking? At most you'll get the canned "It's in the works" response. If they said they are going to do something, then they'll do it. Until then, go outside and enjoy life or fly something else.