This is clever.
I wish researchers would be honest and say they did it because they could and someone paid them to do it rather than making up a whole justification.
The reason psilocybin is not available medically is not anything to do with manufacture it is to do with regulation and prohibition.
There is a claim circulating that pharmaceutical grade psilocybin is 2 USD per mg to synthesize, a lie, the triptans are more complex to manufacture and they are 10 000x cheaper than this supposed psilocybin price, complex triptans are about 100 to 150 USD per Kg for pharmaceutical API grade.
Cultivating fungi and extracting the psilocybin is going to be the absolute cheapest option to get pharmaceutical grade psilocybin, followed by synthesis. An unstable transgenic E coli starting from an unstable expensive feedstock is not going to compete on many levels. The instability will make it very difficult to create a DMF with consistent impurity profiles. This is an academic curiosity.