I wish this were true, but the i.MX 8M Plus is a very different chip than the i.MX 8M Quad. It has added an NPU, ISP, DSP, 3D audio, video hardware encoding and secure keys, which means that it will take a lot of work to fully support it. Another problem is that an additional chip will need to be added in order to convert from HDMI to DisplayPort Alt-Mode. See: FAQ: 7.1 What will be the changes in the Fir batch and should I wait for it?
I guess Purism could use the Plus without supporting those new components, but using the ISP and video hardware encoding would substantially improve the camera and make it a lot more energy efficient.
The biggest advantage of the Plus is the fact that its FinFET 14nm node size should run cooler and consume less energy, compared to the planar 28nm in the Quad. In my opinion, the poor battery life and the excess heat are the biggest problems in the Librem 5. I would like to see Purism use the 800MHz secondary processor in the Plus to implement a new low power mode for the phone. That would dramatically lower the power draw for many tasks, and would allow the phone to receives messages over the WiFi that it currently can’t do when suspended, and avoid the problem with the cellular modem not always waking up and taking too long to wake up.
However, it will be difficult for Purism to raise the funds to undertake a redesign of the Librem 5. Purism can’t use crowdfunding to finance its new projects any more, due to the reputational hit that it took with the Librem 5. If Purism had the finances, it probably would have designed the Librem 11 based on the i.MX 8M Plus, rather than using an ODM design with an x86 processor. I’m hoping to see the Fir based on the Plus, but I’m skeptical that Purism can get the finances for it, and the market will be small for it.