When we had less info from the club, I would have been more in agreement with you. However, over the past year or so, certain things have made me think that 50K+ would be quite easily achieved for a club with our fanbase.
60K is basically the new 50K in this era. For years a lot of people were led to believe that Newcastle getting 50K+ was some unbelievable achievement because quite simply, no other clubs had been able to see for themselves if they could get those types of crowds. The best comparison we have to use for our circumstance is Man City in 2004. They were a North West Club with a fanbase of a similar demographic to ourselves, shared a City with a more successful media darling club and had been starved of success for years. Over history they had lower average crowds than Everton and had suffered multiple relegation's in recent years. After coming 9th (our current position) they moved to the Etihad and went from 34k to 46K.
If they could get an increase of 12K then why couldn't we? After coming as low as 16th in their first season they averaged 45K the next. That is purely down to the New Stadium enthusiasm. It would take Everton to have about 3 consecutive seasons like this current one for crowds to be at risk of dropping far lower, and even then if we get the ticket deals right, the drop off may not happen. Look at West Ham and how annoyed their fans are with their Stadium which won't be anywhere near as good as ours once done, and they have sold 52K season tickets.