I'm not sure if only the client does the padding, or if the padding also occurs at intermediate hops, but Tor does randomly pad traffic by default (from manpage of torrc):

       CircuitPadding 0|1
           If set to 0, Tor will not pad client circuits with additional cover
           traffic. Only clients may set this option. This option should be
           offered via the UI to mobile users for use where bandwidth may be
           expensive. If set to 1, padding will be negotiated as per the
           consensus and relay support (unlike ConnectionPadding,
           CircuitPadding cannot be force-enabled). (Default: 1)

       ReducedCircuitPadding 0|1
           If set to 1, Tor will only use circuit padding algorithms that have
           low overhead. Only clients may set this option. This option should
           be offered via the UI to mobile users for use where bandwidth may
           be expensive. (Default: 0)

Padding is always positive. That means every packet will always have its size increased, but never decreased. With a mixture of packet sizes, and flows, it's still only typically ~30 or so packets to identify a flow with this padding. That means a typical user might have anonymity for perhaps 1 additional second using this option...

Basically - this option doesn't serve it's intended purpose.

I took class in IT privacy back in the day. Exactly this idea came up. And while it really disables certain kinds of timing based attacks, the problem is it doesn't scale. If everyone did this, it seems the network would be flooded.

Is that individually tunable, or are you suggesting something that the project would have to change in their code?

It would only be effective if at least some proportion of clients used it.

If just a single client used this option, their traffic path, all the way to the exit node, would stand out to any network attacker.

Submit a pull request then.