Rapid response technology is close but not there yet. It would require constant satellite surveillance for heat signatures (which we either have the capacity to do today or will within 5-10 years). Beyond that you need a swarm of autonomous heavy lift drones that can fill up and actually carry enough water which likely requires better batteries to be economical since today's best heavy lift drones are limited to a few hundred pounds. I do expect it to be something we're close to having though. Beyond that ideally you would want some form of AI to check to make sure it is the start of a forest fire and not something else (this should be pretty easy given burn bans and fire spreading and such) If we could respond to forest fires really quickly they become a lot less of a problem and it would allow us to grow forests again to help with carbon capture (forest fires release all the carbon captured from said forest).

I suspect once its feasible it will be done fairly quickly because as you said forest fires are becoming extremely expensive and well life altering so the economics and demand are definitely there.