Scriabin's Fantasie 
Actually I have no idea how about its technical difficulties, derp. I just love it 
Maybe something not Romantic, since all the stuff you listed seems to sit in that era (or at least is very romantic-ish). Some late Debussy or or a more modern composition, some Bach? :shrug: I'm sure you'll have more than just romantic stuff once you decide on all your pieces but... I was really no help was I 
Perhaps look at Carl Vine's Bagatelles? His collection of 5 seems to be quite popular lately.
that fantasie is my favorite scriabin work for solo piano. it is unbelievably/insanely difficult, i sooo wanted to work on this in the spring but i did some soul searching and had to , w hesitation, shelve it for the time being until im ready for it.
i agree w your assessment that it would be a great work to include if the op has the base and instruction to pull it off.
i would not reccommend any rachmaninoff or early/middle scriabin though as the op is already playing the warsaw concerto, so style wise i think this 'sound' is already taking a fair amount of performance time (if the op is doing the two piano reduction or w ensemble, then about 10 minutes give or take on final tempos, the solo version i believe is quite a bit shorter).
i would actually encourage the op to open with a short set of scarlatti sonatas, especially if there is not already a larger sonata already programmed.
i would also look at maybe some gottschalk and/or grainer (though heavy lean to tonal/romantic based, i think style wise they can provide some nice contrast, especially if the program opens w very early works as mentioned above).
Topic: senior recital selections?