For all the love the Surface Pro gets, just at the moment I believe the Surface 3 is the most important device Microsoft has released in the Surface line. Unlike previous non-Pro Surfaces it runs full Windows. Unlike other non-Pro Surfaces it supports pen input. Unlikely other any other Surface it is fanless and can charge from a standard phone charger.
For a portable machine that last item is insanely useful. iPad users know that if they run short of power there's likely to be a friendly Lightning charger somewhere around. For Surface 3 users that's true to an even greater degree because of the huge number of devices which use the micro-USB standard.
That most modern phone chargers are powerful enough to juice the Surface 3 quickly is an added bonus - one that isn't necessarily true for iPad users leaching off an iPhone charger.
The Surface 3 packs a useful extra punch in that micro-USB port, because it sports USB-OTG, so with a small adapter it's possible to use two USB devices at once.
Finally there's the LTE option, which allows the Surface 3 to be fully autonomous, something that not enough Windows 10 devices offer.
The slightly smaller, lighter form factor and excellent battery life allow the Surface 3 to be thought of as a true iPad competitor. Add in real computing capability (rather than apps), memory expansion and a significantly better price than the equivalent iPad Pro and its hard to see why Microsoft hasn't replaced the Surface 3 with a warmed over Surface 4, in the same way it freshened up the SP3.
Most likely that was the result of Intel killing the Atom processor, leaving Microsoft with the Core m3 version of the SP4 as the closest thing to entry-level in its tablet line up. Whilst that model looks good value compared to the iPad Pro 12.9", Microsoft has nothing that competes with the 9.7" version.
That needs to change - and the device to do that may not be powered by an Intel processor at all. Rumours of a high-end Surface Pro 5 powered by an AMD Ryzen processor might be interesting, but I think its more likely that Microsoft would tap AMD for a low-power CPU for an entry level device. Especially given the way it has managed to boost performance of the latest Windows 10 Creators Update version on low spec hardware.
A Surface 5, packing an AMD processor and all the Surface 3's benefits, would make an ideal device to hasten the iPad apocalypse. But only if Microsoft makes its move before Apple covers its tablet exposure.