Would it be OK if has become a set phrase used for politeness. The conditionality of the word
if is almost absent, and the phrase is in reality just a weaker, more tentative version of
Is it OK if.
Because of this, it seems to have the force of a present tense in
meaning, if not in form. I think this is what makes a present
tense seem natural after
Would it be OK if. Others may have a different explanation.
Other mixed conditionals -- where no politeness formula is involved --
do not so easily escape sounding at least a little odd, such as:
If he wins, I would ....
If someone says ... , would anyone notice?
If I give you ..., would you ...?
CJ