That rule of a non-paying hand certainly cuts the potential value of
a four
to a royal promo. Looks like 20-23 is the range of the 47 cards
left that will
disqualify the hand.
It looks to be 22-23 to me:
(a) KQJTc:
3x9 or 3xA will make a straight (might have discarded one)
2c-8c will make flush (might have discarded one)
high pair: 3xK, 3xQ, 3xJ (might have discarded one)
the 9 of clubs will complete a straight flush (would not have broken that)
Ac will make the royal, but then we don't need this stuff. Let's just
consider the 46 remaining cards that don't make the royal.
Total: 6+7+9+1=23, 22 if broke a straight/flush/high pair
There are similarly 23 of the 46 (exactly half) where the hand is made
as dealt. So half the time it's 23 that will end up paying, the other
half 22, for an average of 22.5.
(b) AKQJc:
3xT will make straight
2c-9c will make flush
3xA, 3xK, 3xQ, 3xJ will make high pair
Total: 3+8+12 = 23, 22 if broke straight/flush/high pair
Similarly, an average of 22.5.
(c) Other ace high, e.g. AKQTc:
3xJ (etc) will make straight
2c-9c will make flush
3xA, 3xK, 3xQ will make high pair
Total: 3+8+12 = 23, 22 if broke a straight/flush/high pair
Similarly, an average of 22.5.
Although there are 3 suits for the discarded card (e.g. Jh, Jd, Js),
you only discard one of them (say Jh), and you can still draw one of
the other two (say Jd) to make a high pair. Also, the "might have
discarded" cards don't overlap, so even though there are three classes
of card you might have thrown away, whatever you discard is a member
of only one of those classes (e.g. it make a straight, or it made a
flush, or it made a high pair; never more than one of these). The 9 of
club is a special case where it makes a straight and a flush, but then
you have a hand worth 50, presumably way more than a 4-card royal is
worth (some 20), so you would not discard the 9c, and all this doesn't
apply.
Obviously, the same goes for the other suits; I just used clubs as a
concrete example.
So it's 23 half of the time, and 22 for the cases where you break a
made hand (let's hope that *they* are not disqualified as well... I
don't think so, this is supposed to be compensation for a "bad beat",
and throwing away a flush to get nothing sounds like a bad beat to
me). That's very close to half the possible draws (actually exactly
half since the Ac completes a royal, and a royal is most certainly a
paying hand, so really it's 23.5 out of 47, not 22.5 out of 46). Four
to the straight flush is such a damned strong hand 
M.