5 years ago I would say no, but the processors and RAM usage needs have decreased sharply in the last 5 years. There really isn't groundbreaking technology on the way. Intel seems to be focusing on efficiency gains and not raw power. Kind of hit a wall in that regards. If I got 8gb today, I'd be fully confident the computer would be serviceable for the next 5 years. The old conventional wisdom does not really apply the way it used to.
Not to belabor this point, but I'd be more concerned about usb-c peripherals. Not that usb-a peripherals won't be available, but you'd be shut out of the good stuff in the next 5 years.
Agree with
@Sanpete, I'd go with the 8gb TB. Ports on 2 sides being the sleeper killer feature of the TB model that I never considered at time of purchase. Another point about 8gb over 16gb is that it will theoretically use less battery power. Whether it's significant or not is another debate I don't care to get into.