Hi,
I have trouble finding info about the trick where you pretty much only hear the strings of an acoustic guitar. A good example is on the track below. Does anyone here know how to achieve this properly? Is it simply a HPF, or is there more to it?
 
https://youtu.be/k4V3Mo61fJM?t=1m34s

Not sure if this is what you mean but it has been said if you are recording an electric guitarist and the amp is somewhere else but the guitarist is in a quiet place, you can record the sound of the strings being played right up close acoustically.  Then that sound can be added in to the final electric guitar sound. It is supposed to add some more realism to the track.  Personally I have not tried it but it may be worth experimenting with it at some point to hear how it sounds in reality.
 
As for acoustic guitars you are hearing the strings anyway when you put a decent microphone in front of it!  That example is nothing more than a well recorded and mixed acoustic. 

It's a well record acoustic guitar, probably recorded with a small capsule condenser mic with good mic placement so it's not muffled or muddy. 
The other instruments cover up most of the bottom end, but its still there.

Jeff Evans
As for acoustic guitars...  That example is nothing more than a well recorded and mixed acoustic. 

+1

If you want to hear more string sounds with less body then use a sound hole cover. Other than that, use an EQ to thin out all the warmth.

Finally found a bit info about it (or rather another discussion)...
For anyone interested:
http://homerecording.com/bbs/general-discussions/mixing-techniques/getting-stringy-strummed-acoustic-guitar-sound-363111/
 

The link didn't work for me. 
Anyway, it's also about picking right kind of guitar and strings.

Sorry link now fixed

This video basically reinforces the link you posted above https://youtu.be/cZRnrA5GOx0 (6:35 in duration). The more directional a microphone, the more you can focus on the 12th fret area than the sound hole (or even cover the sound hole as mentioned above). Depending on what you are after, you can blend or adjust as necessary for the capture. That video is nice because it talks through some of the mechanics for folks new to recording acoustic guitar.
 
Also, depending on venue, the sound hole cover can save your bacon in a feedback scenario.

They got a great sound! Here's what I'd try: create a copy of the acoustic track then insert EQ to try and bring out where the initial attack sounds the strongest, then run it through a compressor to additionally bring out the string/pick attack. Run these two in parallel and blend. This, of course, is trying to fake it in the mix. I've always found acoustics to be difficult record if you're going for continuity between tracks but what's great is that you can find many different sounds. For example, if you mic around the 12th fret and strum over the neck/body 'overlap' I think you'll get something close to the video you provided.