OK, then who gets Caster-Sakura, if anyone does?
All of this is made much more interesting by the competing agendas of the Servants, i.e. Kaleido Ruby wants Rin to embrace her magical girl side and date Shirou, Servant Sakura wants Master Sakura to stand up for herself and take Shirou by force if necessary, Guardian EMIYA either wants to get together with at least one of the Rin's or Sakura's or if he's more intelligent a way to solve the mess without seeing Fuyuki go up in flames (again) this time at the hands of a furious rejected Caster.
Speaking of Illya, is there any plausibility in the thought of future-Illya becoming a Counter-Guardian?