I wouldn't analyse the English so. Are you suggesting that ‘so’ is an adjective meaning ‹true›, so a more long-winded way of putting it would be ‘I hope [that it is] so.’, meaning ‹I hope that it is true.›? If so, I disagree; I take ‘so’ to be an adverb meaning ‹thus›, so ‹I hope thus.›.
(I've tried to use ‘so’ in as many ways as I could in the previous paragraph. ETA: Apparently, that's too much fun for some people to handle.)