Some time ago, i read about this new disc technology being in research, the holographic discs.

I don't remenber all the details, i think is something like capacity to hold 1tb and very fast reading.

Someone can confirm please! 

Aren't Flash Drives much faster than Blurays/Hardrives?

Hmm, I don't think so, not to my knowledge anyway.  There might be some high end USB 3.0 Flash drives that would read faster than the 6X Blu Ray drive would in the PS4 but I'd be amazed if any were capable of reading at Hard Drive speeds.  Unless of course, you mean SSD drives.  But that would never be financially viable as a means to buy media "in a box" as it were over the counter.

I'm not too sure but I've read somewhere that an average hardrive can go up to 200MB/s while we already have 260MB/s Flash Drives.

You right lol  Ive just looked, shows how out of touch I am with flash drives!  In that case they would certainly work and a read speed of 250mb/s is certainly more than enough.  The question then is whether it would ever be vaiable price wise.  When you factor in that mass printing off a Blu Ray might cost I dunno....$1 a time perhaps, a 64GB or above equivalent in a flash drive would be at least ten times that amount at a guess.  I suppose if the extra cost didn't get passed down to the consumer, I'd be all for it.

With the console market evolving in new and different ways (becoming a multimedia center, streaming, unified handheld-home console...), the digital media is going to overtake the phisical market in an undefined future. However, most of us wouldn't accept a full digital-only console right away. But what if someone makes a digital only console next gen? What if someone makes a model without DVD reader at a price 100€ cheaper? Would that be interesting to the consumer? Which company would try it first?

EDIT: What I meant was some company releasing their console as usual but, alongside the regular machine, releases one model without DVD reader that is 100€ less or cheaper. A digital only console is too far away in the future.

Yeah, but we're still years away from next gen. I'm sure that 128GB Flash Drives would barely cost anything by then.

Having said all that though, I'd still prefer a disc based solution if it was possible.  Nostalgia and all that!