2020 is only 7 years from now. Seven years ago what did the average system look like? Well, that was the year the Core 2 launched. A lot of people are still using those systems. Computers kind of reached a "good enough" plateau at the time. Meaning that the laptop I bought 5 years ago with it's 2ghz Core 2 still does everything your average user does with a computer, without noticeable performance impact.
^^ These were my thoughts as well; the main booming techs right now for computers are multi-core CPU's, integrated graphic GPU's on the CPU die, and SSD's. Speed of CPU's has only incrementally gone up the past 7 years.
Realistically, we'd be talking Intel going through another 2-3 "tick/tock" iterations, which means that they would be more aggressive at going after the tablet / smartphone market and the GPU / mobile PC market. They also have the M-SATA drives coming into the market, which have pretty incredible performance specs for such a small device.
My main thoughts is that PC's will be scalable; all the way from a smart-phone sized-unit to a full blown PC unit. Each set of items will be able to be plugged into a dock that acts as a full PC (we are already almost there, so it's not a big stretch, especially given tech like Thunderbolt). So you'd have the full PC experience with your smart phone, including games, a full keyboard, a 4k monitor, mouse, etc. and then be able to unplug the smart phone when done using it in that way and bring it around with you.
By scalable I mean everything from a smart phone that can run basic games on a 4k screen, to a tablet, to a ultrabook, to a notebook, to a mobile workstation, to an HTPC, to a medium sized PC, etc.. Docks that have a thunderbolt input that can take any of these items, and wireless tech such as widi (intel's wireless display tech), etc..
Basically any level of size / power you want, you can get. With mSATA drives being so ridiculously small, I picture tech like RAID-5 in a large notebook (alienware already has RAID levels for notebook drives, with MSATA being so small you could probably squeeze 4 drives in a laptop fairly easily). Scalable CPU's in the form of add-on cards, based on Intel's own super-multi-core Xeon cards, and more built into the CPU itself directly. This would allow for ray tracing-based games to finally hit the market.