Well there's got to be a limit somewhere, if 90 character channels were allowed then what's to stop someone coming along and complaining that 10,000 character long channel names aren't allowed? 90 characters is WAY beyond a practical limit.
Nobody would ever type in such a long channel name, and it would be impractical in most displays even to click on. Why on earth would you subject people to that? It's not like you can say that all channel names below 90 characters are gone - if only 10 characters were allowed using english alphanumeric there would still be 3,656,158,440,062,975 possible channel names. Granted, most wouldn't make sense but if given the choice between #zfhjjhzjhd and #hello_there_this_is_my_very_long_channel_name_which_is_readable_and_makes_sense_do_you_like_it I'd take the short non-sensical one every time.
