We also know from personal experience that airline check-in clerks can be fussy about following rules, more so than immigration officials. So if you do show up without a confirmed onward ticket out be prepared to be refused boarding, or be sent back after arrival. Them's the rules!
There is no risk in providing an easy-to-digest plan to the airline plan and a separate --more ambitious, but still compliant-- plan to immigration. Note, this is different than providing a safe plan to entrance immigration and changing it on the fly (I would NOT do this).