Honestly I think the effect is progressive enough already. Aside from the Viper which goes into high Gs quite rapidly, others just have the effect appear gradually, but even when it slightly turns red (or black), you're still a long way from reaching the limit.
It serves as a proper "warning" that you should go easy on the stick, I don't think a bar or number would be better, nor even needed most of the time. It's not like it happens often anyway.
Albeit I'm curious why collisions which send you into an uncontrollable spin don't actually lead to a loss of consciousness despite their brutality.