And to be a bit more specific--seeing how I doubt that every OT Feature will ever make it into XDP (at least for a bazillion years)--I would like the following, not quite in a specific order but close.

(1) Stylistic Set Support
(2) Contextual Alternates
(3) Ligatures
(4) Access All Alternates
(5) Swash
(6) SALT
(7) Discretionary Ligatures
(8) Fractions
(9) Old Style Numbers
(10) Medial and Terminal Forms

Ought to be several years work there...