Hi
The 0.65mm pitch part is designed/intended for 4 layer boards and the NXP EVKs are 4-layer designs allowing all pins to be used and also (according to them) passes FCC tests.
The only drawback is that some room around the device is needed for fan-out of the signal lines when many are used and when some GPIOs are not needed that means that it can be packed tighter together. See the attached screen shot of the chip on the NXP layout. 6-layer board would probably alleviate this.
NXP also has a detailed design guide at
https://www.nxp.com/products/processors-and-microcontrollers/arm-microcontrollers/i-mx-rt-crossover-mcus/i-mx-rt1050-crossover-mcu-with-arm-cortex-m7-core:i.MX-RT1050 "i.MX RT Hardware Development Guide for the MIMXRT1050/MIMXRT1060 Processor"
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It is undeniable that more board layers and working with finer pitches and smaller holes will increase the price of a PCB and it is up to the designer to decide on such tradeoffs. However, in comparison to a K66, which - if it can be found and purchased at its normal price - tends to be much more expensive than an i.MX RT 10xx - maybe in the order of $10..15 and, coupled with much more peripherals and performance even paying more for a PCB should result in a cheaper (and potentially) better product.
I have also attached a screen shot of one of my designs where I use 77 ports/GPIO plus 1 x USB.
Regards
Mark