To start with spraying now has rates of at least 30 L/Ha and often more. To spray in commercial quantities you need capacity, not a 50 litre load. There is the technology now to make an Ag aircraft pilotless, fixedwing Ag aircraft are now worth up to 1 million, rotary to carry anything more than 1000 litres maybe 2 million. To make that aircraft pilotless you need another million in electronics and software.
Then you still have to pay an expert to fly the aircraft remotely who would no doubt charge more than an Ag pilots whose wages haven't gone up in 40 years.
The military have very capable pilotless aircraft with good useful loads, they pay 220 million each for such capable machines.
Yes it's possible, economics and reality make it unlikely anytime soon.