I keep an eye on it to see if anything changes, I haven't noticed many microsoft replies since it was determined that replacing the battery in the pen wouldn't change things.
From my experience(and reading), it depends on your drawing style whether or not the diagonal lines cause you problems. If you draw quickly there is no problem, however, if you try to move slowly the waves show up. I tend to draw on the slower side, unfortunately. Best bet is to try and find a demo at a microsoft store, or bestbuy(ish) store. Try it with your normal drawing method and see if it is a problem for you.
I've been trying to find a "perfect" drawing tablet for years, there is always some trade off happening. Just got to pick the least annoying one. I've been using a Surface Pro 1 since it came out, and haven't had any major troubles, and I may try the pro 4 eventually.
It seems to be more a problem with the N-Trig digitizer than the device itself. I'm still debating on the surface pro 4, it seemed less of an issue to me on one I tested, but it's hard to tell. It is nice to just have a small tablet to carry around rather than a huge laptop. On the pro 1 I've had drawing apps, programming apps, even SQL Server running happily. It is definitely a solid system. I ran out of space a few times, I won't cheap out on the hard drive next time :)
A good place for reviews and news is http://surfaceproartist.com/ they have reviews of many different devices, not just surface.
Hope you can find some good info.