Any company that provides travel carriage and charges you extra money just to bring luggage is not going to spend a dime on technology when flight attendants can do the same thing at no additional charge.
Considering, too, that seating arrangements aboard airliners is pretty variable… not specifically fixed at design time. Seats bolt into tracks. They can be added or removed, and spacing can be adjusted, during maintenance. So the wiring harness itself would have to be set up with pigtails for the maximum seating density allowed by space and weight considerations for the airframe, and the maintenance crew would have to play with hooking up seats to the harness… and you’d have to protect the wiring, both connected and not, from feet and luggage and the like.
So, yeah, increased complexity and electrical hazard exposure? Absolutely not. The risk and cost element renders any concept of “technical feasibility” utterly irrelevant.
I don’t think that is an issue. Most airline seats already have in-flight entertainment of one sort or another built into them. The wiring for a seatbelt notification system could easily be piggy backed on what is already there. But why send it all the way up to the flight deck? Why not just have a red light above each seat that extinguishes when the seatbelt is fastened? This would have the benefit of being easily checked by a flight attendant by just looking down the isle, and of applying peer pressure to the offending passenger as they know that everyone else can see they are the one holding up the flight. Ultimately though I think there just isn’t any need for anything like it.
How would the pilots know which seatbelts were not fastened because there’s no one in that seat…
Maybe they could have the flight attendants check. That way the pilots could find all of the unfastened seat belts, and then tell the flight attendants. Then the flight attendants could check each of those seats to see if it was empty and then tell the pilots. Then the pilots could figure out how many of the unfastened seat belts had passengers in them, and announce it to the flight.
As suggested earlier, a weight sensor in the seat, just like what a car has.
Seriously though, although the entire aircraft including the cabin and passengers is the captain’s responsibility, the responsibility for control of the passengers is delegated to the cabin crew. Unless something really untoward happens and the captain needs to know about it, what happens in the cabin stays in the cabin. It is possible that someone might decide a seatbelt sensor is worth having, but there is no need to involve the flight crew.
That is extra work and lots of communication back and forth. More likely the airline would install something that the attendants could check themselves.
In reality, that is never going to happen, since you have to check up on the signal by walking down the aisle, you might as well just skip that and… walk down the aisle, glancing left and right at every seat. Just like they do.
Airplanes aren’t the only things that go whoosh.
Some airline seats have a little light that tells the flight attendant if you’re in the upright position
I was on a flight yesterday (~40 person aircraft) and they had to boot two people off in order to put the extra baggage into their seats (and to solve the overweight aircraft problem). They used a tactic of “Whoever here is the most scared of flying? Come with me as you’re not going to want to take this flight.” Which was incredibly true as it was one of the roughest take-offs and flights I’ve experienced. Only an hour, but they still never turned off the seatbelt sign or allowed electronics and pleaded that all bags remain stowed.