I think 24,000 is the realistic maximum number of season ticket sales possible. At least in terms of big round numbers.
It’s been pointed out above that South Stand season ticket holders have to be accommodated in the main East/North/West bowl for FA Cup games which limits the total number of General Admission season tickets to the total available in that area.
There’s about 23,200 General Admission seats (including family and premium zones but excluding hospitality) in the East/North/West stand bowl and at least 200 of those can’t be sold because they aren’t available for live TV feature games. The club also choose not to make Block 5 available for season tickets, presumably to give options for segregation, which is about another 200 seats.
Hence to sell 24,000 season tickets requires about 1,000 to 1,200 hospitality seats to be sold as season tickets which is pushing the limits of what’s likely. Club Coventry, Legends Lounge and The Mill is about 1,000 seats combined.