Well someone had to pay for the Allams' pay rise, and everyone else's pay cuts obviously didn't quite cover it.
Re: the family guarantee Yes the leaflets did say that it was a guarantee families would not pay more than 2015/2016 for their first year of membership, however, the Terms and Conditions were the standard ones and thus I believe the club will have to give 90 days written notice of any change in price.
That 90 days is the key. There will be no new price for next season as it's not a season scheme. It's a monthly scheme & as such the cost is a monthly price. People are fee to leave the scheme at any time & they can alter the monthly price at any time, so long as the t&c are satisfied.
For what it is worth, and I am not sure whether it will have a bearing on general membership/passes next season, but I got a letter today saying my corporate membership fee has been frozen and it is the same level as this season whether we are in the EPL or Championship.