I've done some looking around and it doesn't seem like Marvel has released or has any plans for an Excalibur omnibus edition. Given that I'm sure they've done Omnibus editions of less popular series, this seems strange.
My impression has generally been that Excalibur is fondly thought of by comic fans and I certainly liked it a lot.
Would anyone else be interested in an hardback omnibus of Chris Claremont and Alan Davis' (plus Alan Davis solo) run on Excalibur, or is it just me?