I can only imagine the word ‘бывший’ as a noun (with the meaning ‘ex-husband’ / ‘ex-boyfriend’). The other words (‘следующий’, ‘текущий’, ‘будущий’) are not used as nous, IMHO.
Well, you can use any adjective without a noun, e.g. «Последний был лучшим» — “The last one was the best one”. But, I think, this is not the same as ‘рабочий’, ‘мороженое’ etc. In such phrases adjectives remain adjectives.