Srimate Ramanujaye Namaha!
Interesting question and also interesting answer given by Kambandasan swamy.
To add other perspectives to the discussion.. what Swami said in enpani 1796 (or you tube video no 1795) may be relevant in this discussion also.. though having no karma is a requirement for moksha, desire to serve is also a requirement for being in vaikunta.
Secondly, instant moksha if given will baffle atheists and they will not be able to continue to exercise their free will and say that God does not exist.
Thirdly, we may do many things which ought not to be done and and to escape that we may want moksha , instead of really wanting to serve.
Also in another angle, for a surrendered soul, even if he is physically here, he is actually liberated from the effects of karma in the sense that whatever happens, out of his past karma, he is able to remain focused in his devotion and service to Perumaal. In that sense such a surrendered devotee is already in Vaikunta (place of no anxiety).
Kambandasan swamy: In placement offers, some companies give offer letter with clauses attached..”subject to not having arrears in the upcoming semester etc..” are such clauses applicable in this case as well?