I just received a response from Geiselle on the development of a trigger dedicated to the MPC/MCX. It follows:

Thank you for contacting us. In regards to our stance on our triggers in the MPX and MCX, as the industry grows, there are more and more AR variants out there that accept AR15 fire control groups. Each one is different and though we would like to, we have not tested our AR15 triggers with any of them. What we know about our triggers in the MPX we have learned from feedback from our customers. From the beginning, our customer service representatives have explicitly told people that we have not had any experience with our trigger in the MPX/MCX. We have stated that forum users have claimed to have success but we cannot confirm their success. We have never strayed from this and have never confirmed our trigger work in those platforms, and have always maintained that our triggers were designed to function with a mil-spec M4 carbine. With that said, the MPX has a very fast action, which is why the MPX ships with the trigger bridge, to protect the fire control group from the action. The MPX was designed to be used with the trigger bridge, our triggers were designed to be used with AR15 rifles using mil-spec components. While the MPX combination will work for a while, it will eventually fail. We want to be clear with our customers on this, and also have them know that we are working on an MPX specific trigger. We do not recommend using our AR15 triggers in these variants as it will void our warranty.

Going forward, rebuild kits for our AR15 triggers installed in the MPX/MCX will be available for a fee. The SSA-MPX dedicated trigger group is currently in development and will incorporate a trigger bridge to alleviate the current issues. It is slated for release in 2017. Unfortunately the SSA-MPX trigger is still in development and the price has yet to be determined as well as a definitive release date. This trigger will be for both the MPX and the MCX variants.

As for the recent MCX recall and the new carriers, we have just recently heard of this recall and we are still working out all of the details. Right now, we cannot confirm this information. Once we get more information about this issue, we will let everyone know. I hope this helps. Please Let us know if we can be of further assistance.

Thank You,
Charlie

Seems pretty clear to me. I am happy to wait a dedicated trigger into my MPX.

Thank you, Charlie.

Thanks. I like your triggers. They are worth waiting for. Just don't make it too long. I am old.
And if you want a tester, I am available.
Tommy