Kaioken is not a state or transformation. It is a special technique which multiplies Goku's power. Assuming Kaioken doesn't have a limit and you could reach a multiplier beyond 20, Goku doesn't necessarily need to keep utilizing the same to get used to the state. This is because Goku has to train his body to be able to adapt to the physical strain imposed by Kaioken. This requires excellent Ki control which is why Goku was able to stack it on top of SSJB and we never see him stacking it on top of SSJ2 or SSJ3 when he fought Beerus or Back in the Buu Saga against Kid Buu.
Also, it's been stated by Whis to Vegeta that God level training involves excellent Ki control and not just putting your body through a lot of physical strain. Also, Kaioken acts as a multiplier to Goku's current level of power and not his Base form unlike his other transformations. So in other words, if someone were to train and achieve a stronger transformation which is a higher multiplier, having a higher multiplier of kaioken wouldn't make a difference.
Suppose there existed a transformation which was a lot superior to SSJB(Not gonna use UI here), which is a significantly higher power multiplier than SSJB, then even 30 times SSJB, will not be able to stand up against that power.
The best way to illustrate the same would be with an example. Let us assume Goku has a power level of 2 and let there exist one transformation which is a 100 times multiplier and another transformation which is a 200 times multiplier. If Goku utilises the first transformation and is capable of using Kaioken * 3/ his power would be : 2*100 * 3=600. Incase of the second transformation, let's say he can only use Kaioken * 20, but his power would be : 2*200*20=800. (Please note these are not actual power levels and it's only an example to prove the same)