Drawback of using Schottky Diode to lower MOSFET threshold voltage?
This cannot work. It is not possible to lower the threshold voltage. The threshold voltage can only be increased by having a voltage between backgate (bulk) and source. See the relevant article on Wikipedia.

If there was some way to lower the threshold voltage of a MOSFET through a "circuit trick" then for sure I would know and use that trick. I've been dealing with CMOS circuits for more than 25 years.

The only way to lower the threshold voltage is to change the physical properties of the MOSFET (doping, oxide thickness etc.).