The key to making a lot of money with inscription comes from combining the sale of Contracts with the sale of Glyphs. It’s not uncommon to see some Glyphs swell to 4000% of their normal value during times of increased scarcity. This means less stable income but much more lucrative prospects. Even though this guide assumes you are pairing Herbalism with Inscription to farm your own mats, under certain conditions it may be a better idea to purchase the materials from the auction house.
I think what you're actually talking about when you say "niche" is the barrier to entry for new players. It sounds like you're worried that new players can pick up crafting professions and compete easier than before. Again, I'd say that the alpha build info in the OP looks pretty much the same as the current expansion. The true barrier to entry isn't the ability to level the profession quickly, it's actually recipe ranks. Some really good examples of this in the current expansion are rank 3 bracers, rank 3 flasks, and rank 3 felwort. It takes a certain level of investment to get those ranks, and the goblin activities related to those crafts simply aren't profitable/competitive without rank 3.
Sorry about the salt but jeez, stop listening to guides. Just check your AH, see what old mats are low in offer, and go get em. >FOR EXAMPLE<, ghost iron ore is a gold mine right now, cause nobody can sustain the demand, and prices are way up. Plus side being, old farms are optimized like hell. You can fly in the old world, mobs won't bother you, no one is there to take your nodes, and there are plenty of items to make the most out of it. Which means it's way easier and requires less effort than farming in BfA.
Yes, that is easy, but it's not quick. Further down in my comments to OP I detailed the GIO farm, and reasonable yield expectations. I looked up a few guides/videos before commenting and most of them estimate a yield beween 800-1,000 GIO/hour. That lines up with my past experience with it as well. That'd be, taking the high yield end, 4.2 hours to farm the GIO for one toon's monthly needs.