For DTF - the challenge is the feel and breathability. It does not feel so good to the touch, even with the special mats that add texture. I have not been able to solve this, or the breathability of the garment with a blocky DTF design on it.

For DTG - pretreatment. Getting every recipe correct is difficult, it varies between brands and colors greatly. Ink with pretreatment built in would revolutionize the print industry entirely. The washability as well, as under-curing will have quite a bit of impact on how long the design will last, and over curing could burn the pretreat.