I know what you mean, it doesn't seem like 8th has been out long to me either but its been about 4 years. I've heard the rumour of a few giant books for multiple armies in 9th as well, i think it would be a mistake though, i have most of the fantasy armies (of varying sizes) so it wouldn't bother me much if they did it but some people only play one or two armies so i couldn't see them paying a hefty price for a book when they only want the one set of rules/fluff.
From what i have heard its supposed to be Dwarves then Wood Elves for the next fantasy releases. I dont much care about the elves but i hope it is right about the Dwarves, though i have a horrible feeling they are going to end up with a magic phase/lore and it be explained as unleashing magic from runes in a similar way to how bound spells work