I remember it being mention in that spin off with Iylla as a magical girl, girls were in bath and Iylla looking at Luvia's breasts saying she was as big as Leysritt
Anyway nice suggestion with both ideas, yeah I imagine Shirou would do a bit of mind break realizing what he has done not to mention feel horribly guilty as well. Still I like you earlier idea with Saber, Rin, and Shirou end up watching each other as they are being taken advantage of. Makes you wonder when they will simply break down and just enjoy it.
Still among them all I might pity Rin the most having to deal with his violent and powerful thrusts, she is most delicate amongst three of them:)