That is an interesting idea. We have the HSI, but currently we do not have the GlideSlope on it. There has never been a request for an ILS. We'd have to look into this as ILS is frequency and signal driven, not location driven like a NDB or VOR.
An ILS consists of two independent sub-systems or frequencies, one providing lateral guidance (localizer), the other vertical guidance (glide slope) to aircraft approaching a runway. The Localizer and Glideslope are basically just a comparison of the signal modulation by the ILS receivers in the aircraft. The iFly does not have a receiver to read or compare those differences.
I'll put this on our wishlist and for more research as there may be some means of coding the Glideslope and Localizer for each approach, but that might be very time intense for a non-certified portable.
All the iOS apps that have an ILS are basically just trainers, not actually functioning or navigational ILS instruments. What APP is it that you are referring to?