Foreachwiki and friends are available in the Kubernetes container now, with a flag on the way to make it easy to invoke them via mwscript-k8s. (https://phabricator.wikimedia.org/T378479) We've also resolved the resource-consumption issues with the shell loop approach, so that option is viable too.

(That is, simultaneously launching that number of jobs will no longer overload the Kubernetes infrastructure itself; of course it's still possible to use up the available compute resources, and it's also possible -- as ever -- for aggressive maintenance scripts to overload shared resources like the databases. But it's back on the table; consider it remediated from the temporary guidance "don't do this, it's dangerous" to the indefinite guidance "this is powerful, do it cautiously.")

Interactive scripts like eval.php can be used with mwscript-k8s in --attach mode (which forwards stdin and stdout to your terminal). (https://wikitech.wikimedia.org/wiki/Maintenance_scripts#Input_on_stdin) Separately, note there's also mw-debug-repl to get a shell in a mw-debug pod, rather than a mw-script one. (https://wikitech.wikimedia.org/wiki/MediaWiki_On_Kubernetes#MediaWiki_REPL)

That said, mwscript-k8s can't support {my,}sql.php specifically, because we don't have a mysql client in the MW image and shouldn't add one. For now, you can run `sql` from the deploy hosts instead of the mwmaint hosts. The long-term replacement probably won't be a maintenance script at all but a dbconfig-aware wrapper around a local mysql client. (https://phabricator.wikimedia.org/T375910)