The only way to co-exist gracefully with TCP is to use a compatible backoff mechanism. Anything more aggressive will basically steal all of the bandwidth from TCP and that's it.
For a home environment, this would most likely be at the Internet Gateway level, since home networks usually operate at >100Mbps transfer rates between nodes, but to the internet have <=100Mbps.
That all being said, contention at the gateway level like this would be assuming that KCP and TCP are both being used for, say, large file downloads.
If KCP is limited to use for sharing game state data for a game like Counter Strike, then the likelihood that KCP would consume all available bandwidth within a given time window is low, since the data rate is measured in hundreds of Kbps, not Mbps.