737s are a 1970s aircraft and the A320 is 1980s
Yes they are old, but I think most now have some type of tablet (IPad) as part of their EFB and some even have Wi-Fi onboard. I expect they would have the ability to see ADSB -IN through some type of app.
If pilots can use onboard Wi-Fi to view the latest ground weather radar return on their Jeppesen charts, you think they would be able to do the same with ADSB.
However I still think a tower is still the best option.