Would someone who sleeps with the intention of waking up for the congregational 'Asr prayer be sinful, given their prior knowledge of the difficulty of waking up and missing the congregational prayer?

Sleeping before the prayer time begins is permissible, even if one suspects missing the prayer, because the prayer is not obligatory before its time. However, we should note that some scholars have made it obligatory to take measures to wake up for the prayer.