First to be clear (consider this a disclaimer), I am not suggesting that they do not have support for a disc drive at all. As theer are ways that a disc drive a beneficial and going all digital or even switching to carts won't circumvent those benefits. Now onto the thread.
By the time the PS5/XB2 comes around, theer will be a glut of storage options available. But let me just list out the three main contenders for the sake of perspective.
You can skip to the bottom of this post and just read the options if you don't wanna read too much.
- Blu-Ray drive
This has a read speed of 4.5MB/s. Now a 6x drive (as seen in the PS4/XB1 comes out to 27MB/s and an 8/12x drive (as would likely be in a PS5/XB1 comes up to 36 and 54MB/s respectively.
This represents headaches for game design in general and is why all games get installed onto an internal drive. Reducing the disc drive itself to nothing more than a content gate/bridge. Really, they do nothing for the console outside of just providing a cost effective way to get your games to you(assuming the prospect of going digital would be too much of a hassle). - SATA drive
With this we have two options. Mechanical drives HDD (what the PS4/XB1 natively support now) and solid state drives SSD. Ideally, if the hardware is optimized for them, we are theoretically looking at speeds ranging from 150MB/s, 300MB/s and 550MB/s for sata 2 HDD, sata 3 HDD and a sata 3 SSD respectively.You can knock off 50-100MB/s on all drive types to get their real world figures.
By 2019/2020.... the cost of a 1TB (1000GB) SSD would probably cost sony/ms what it cost them right now to get a 1TB HDD. And this marks the first option where a native disc drive wouldn't be built into the system. - NVMe Drive
This has the smallest form factor. And is gaining popularity quickly. It uses the same base technology with SSDs (flash memory modules) but it runs a 4x PCie inteface as opposed to a SATA interface and also has a memory controller and ram cache to facilitate its blisteringly fast transfer speeds. For this we are looking at around 2500MB/s to 2800MB/s speeds.
With hardware optimized for this, no game should take more than 10 seconds to load a level. And that would be even considered slow. It would also do wonders for how game engines are designed as streaming game data for vast varied worlds would become a very viable option reducing the amount of a game that needs to sit in ssyetm ram.
The costs of these drives are also dropping rapidly and by 2020 we could very well be able to have a 496GB/512GB NVMe drive for as little as it would cost to get a 1TB HDD today.
- scenario 1
$399 console + 512GB+ NVMe SSDand no disc drive. But you can use any third party external blu-ray drive or pay $80 for an official external drive. - scenario 2
$450 for the console + 512GB+ NVMe SSD + bundled external bluray drive. - Scenario 3
$450 for console with bluray drive + 1TB SATA SSD. Evrything is built in but you compromise on overall performance. Generally more conveninet though.