Have been thinking about this lately - many method books and educational materials are marked "early elementary" "elementary" "early intermediate" "intermediate", "intermediate advanced" "advanced" etc. In addition there are such classifications as Easy Piano, Very Easy Piano, Simple Piano, Advancing Artist, Big Note, EZ-Play, etc. Confusing, huh?
But for Gospel players the goals are different. Many church musicians don't read, and some don't know the ABCDEF letters on the keys or chord symbols. I think intermediate level for Praise keyboard players should include playing 3 and 4-note major and minor chords by ear in the most-used keys, recognizing the names of the sharp, flat and natural keys (when you say 'A' they should be able to play an A). In addition, they should be able to keep in rhythm and move smoothly between chord changes.
A more advanced player should be able to -
Play and understand slash chords (like D/E), Aug/Dim, suspended, different kinds of 7ths, 9ths, etc., and play in more extreme keys like Db and F#. Jazz training a plus in Gospel.
Be able to do different chord progressions, inversions and voicings. Be able to read the guitarist's chord chart.
Easily find the key of a song they hear, after trying a few notes. Also, transpose without using the button.
Understand the number system (Roman numerals in classical music theory, scale numbers 1-7 in Gospel)
Play with the proper rhythm and feel, don't drag or rush the tempo,and play just enough to blend in with the others in the group. That is, don't overplay, but do the bass line if there is no bass player, be able to put in solo lines and riffs but not at the same time as the guitar, horns and vocals, and do not play so complex that it confuses everybody else.
Of course if they can play and understand scales, modes, theory and read notes that gives them an advantage...