dferrero17

Display is almost the same. Both have P3 gamut, 120 Hz, very bright etc. It's just the rounded corners, everything else is not worth mentioning, if there even is any difference.
Also, both have 4gb Ram (only the overpriced 1TB pro 2018 has 6gb Ram).
More performance is useless atm for 99% of all use cases. My 2017 pro flies like crazy.
 
USB C helps in the long run, because Lightning is dead (thank god... too bad, i still have the 2017 pro).
Also, MUCH smaller bezels on the 12.9" model.
 
On the other hand, headphone Jack on the 2017 model, and a much better Price.
 
 
The 2017 model will not be unbearingly slow. iPads keep their performance for a looong time.
 
 
Let me break it down for you:
If you can afford the 2018 Pro variant, without having problems buying food for the rest of the Month, or paying bills (or coming even close to that); get the 2018 pro. You will probably not feel any difference yet, but it COULD change. More performance is never a bad thing.
 
If it's too expensive, and you can save several hundred bucks, there is no problem whatsoever in getting the 2017 model.
The money you save here can be used to upgrade 1-2 years earlier, if needed. In the long run, it probably might not matter.
The biggest downside would be: 2017 Model has still Lightning, so you might "buy" lightning accessoires, instead of USB-C.
 
Oh yea, and the Pencil.... Not having to charge so stupid via Lightning port is a huge deal kinda... it looks stupid, and it could break if you have a little accident.
Pencil 2 feels better (matte instead glossy), charges Wirelessly by sticking to the side of the ipad with strong magnets... less chance to lose the pencil, or the cap. and no risk of breaking.
And the double tap.
 
 
So yea, like i said. If you can afford it, get it.
If not, the 2017 pro is perfectly useable and still very far from reaching it's performance limit.

I'll be another person that will recommend thinkpad for coding, my friend bought thinkpad t440s i7 something, 12gb ram and ssd. He is on his thrid year of computer science and he is like "Ill replace this laptop, if it's break" In general, if thinkpad comes to you working, on 4-5 gen he will probably be working fine next 5yrs

As much RAM as you can reasonably get + SSD. That's it, that's all you need, everything else (good keyboard, screen) is just comfort. It's up to you to see if it's worth upgrading vs buying a new PC. You could still code on a CPU from 5-8 years ago and be fine with it. You're not breaking technological grounds by coding in general, you don't need a beastly computer.
 
I personally code on a ThinkPad T460, i5-6300U, 8 GB RAM, SSD, iGPU only. If it does not break, I will still use it in 5 years. The only desire for me is to get more RAM, so I wouldn't need to close my browser to start a couple of bigger VMs, drooling over the 2x16GB, will get to buying it soon.

Problem is many people do not simply use text editors, they will use an IDE for large scale projects and some of these softwares are very resources heavy. 

"bootleneck" i'm fed up with the word. how can text editing caused problem with the computer.
Do you have any problem so far using it to code?
If you use it just to code i think it won't have any problems, unless you wanna do virtualization or graphic simulation.
By today's standard a pc should have 8gb ram and a ssd.
If you meet that with a new battery the laptop would be twice better i think.
4200u is still a good cpu. SSD would make it even better.

If it's mainly for note taking, the old 2017 pro will more than suffice for the next few years.  Another recommendation is the current generation iPad Air (with the a12 chip).  On paper, it's faster and newer than the 2017 pro, which should equate to a longer lifespan. 

The new Pro has a better display, much more powerful SoC, more RAM, and USB-C. I wouldn’t get the 2017 model if you’re set on getting a Pro iPad. 

I would advise the dual device route. If possible though, you should get a Mac to compliment the iPad. 
 
iPadOS now gives you a downloads manager, desktop class browsing by default, and access to external storage over USB-C. It’s a very capable laptop replacement for a student who doesn’t do coding (but does not have a PC already).