Right now I'd say I use Youtube a lot - I have subscribed currently to about 60 channels - essentially it's replaced my traditional television viewing. However it's not replaced my reading time, as both offer different pleasures that the other one can't really compete with. I honestly think they can be complimentary.
Yes, there could be a worry that competition from such a source is 'stopping' new blood from getting into books, as we only have a limited amount of time to pay attention to something, and that is true (but then we also have to add in other activities such as Facebook, Gaming etc...)
however, hasn't there always been other activities that got in the way? Sport, cinema going, Scouts/Girl guides etc. Even in the 1970's not everyone read books!
I think Peat, above, got it right, Youtube is a different medium and you have to think differently to do it well. So not only get your video and audio skills up to scratch, but, in my mind, the core of your 'offering' has to be unique and original content. Successful channels usually have a simple and distinct rationale that take advantage of the platform and the video medium. Also a great deal of it is sold on the personality of the presenter.
Yes, there are huge amounts of narrative's on the platform, but they are very different from book fiction - they are mostly spontaneous and visually rich i.e. 'Let's Plays' of computer games.
How an up-and-coming author might take advantage of this, I'm not so sure. There are plenty of channels dedicated to books of well known authors - huge demand for the lore and world-building of big novels or fantasy worlds, - so for example LotR, ASoIaF, Star Wars - not only because people get obsessive and look for all sorts of details, love theories and want a place to discuss them, but they of course have plenty of clips from movies and TV! But these are channels started by fans where the initial fan base is large.
For an unknown author to grow in Youtube, it feels to me it will be a massive amount of effort - even if you have a great idea - that'll mean you'd be neglecting your writing side. I have seen quite a few Vloggers talking about writing on their channels, some even tried to leverage a self-published book out of it (it did not appear to work). Bnt there's a limit to how many '10 things you should avoid as a writer' vids I can stomach.
Also IMHO, I'd be wary about using it as another form of advertising. Say in releasing 'audiobook' teasers of chapters - remember most people hover their mouse over the 'skip' button as soon as any advert appears!
I'm sure something
should work that might benefit your writing, there surely are a great deal of possibilities, but it will probably be doubling your workload and branching out into something other than straight fiction writing.