Guitar can be a frustrating instrument, especially when it comes to learning scales; I spent a fair amount of time woodshedding them but I was always interested in alternate, or even unorthodox methods and ideas for learning scales. My biggest gripe with the 3NPS or CAGED patterns is that it takes a hell of a long time for them to actually become useful because of the quantity of information you need to learn to get to be able to improvise; by which time your hands have become entrenched in the patterns and whatever you play sounds pretty much like scales. So what can you do if you’ve got scale fatigue?
Marty Friedman is an interesting and slightly unorthodox guitarist; in this video he talks about creating your own scales rather than wading through tons of patterns. You’ll inevitably come up with the same scales: harmonic minor, major, dorian etc. but the difference is that you'll feel as though they're yours because you created them—you could even invent your own names for them. When the brain goes down this route of learning it seems to bypass the questioning, critical element and whatever you learn simply sticks in your head, forever. I imagine it’s the same process as writing a tune or a song; as you’ve created it you feel it belongs to you in a way that a bunch of dots on a fretboard diagram will never do.
Check out Marty’s approach in the following video. You’ll notice a couple of other unorthodox techniques here such as his right hand picking posture—no guitar teacher would ever show you that one but it works for him—and his sparse use of the fourth finger on his fretting hand. Try it out!