I wonder if it would be possible to add another track for demo drivers or add a brand new one for S2/S3 licensed drivers and push down one track from there to Demo.

Probably not, Demo is like a taste test-you don't get the full meal

its already just 12 pounds for S2 (Bulgaria) and the pound also collapsed, whats the problem?

I would get it now then, the pound has been on the rise overall this month and is set to improve even more , It is now up 0.7% at $1.23 after MPs voted on Wednesday to pass a bill to prevent a no-deal Brexit. Always best to check the current facts as it forever changing

No, it's not about the price. I was just wondering if maybe a content update is possible. I would love to pay for a license but I don't have a card/paypal balance to buy it.

Quote from BerdyGaming :

I was just wondering if maybe a content update is possible.

Demo version is just for demonstration and testing purposes - to demonstrate simulation physics,graphics and general sim abilities like online mode etc.,and also to test user's hardware to make sure sim runs fine on potential buyer's computer. The current content provide all that perfectly.
From other point of view - you should be happy that LFS offers completely time unlimited demo mode,in most games even that is limited.

Quote from BerdyGaming :

...or add a brand new one for S2/S3 licensed drivers and push down one track from there to Demo.

Any new tracks, cars or other content will likely only be for S3 licensed users.

Well... Hhmm.. Can I mention a certain wind starting with S ending on occo? Should be S1 content ..

Best decision I ever made initially buying S2, have made lots of friends in the cruising community, demo is a "try before you buy" feature, so imo Blackwood and XFG/XRG/FBM is enough, after all, it is free!

In all honesty, the LFS demo has plenty of content already.
Unlimited time and full online access to 3 cars and 3 tracks is A LOT for what is meant to be a "free tryout".
If you want more cars, tracks and other features, buy the S1/S2/S3 licence to support the developers, or try to win a voucher in one of many contests held on demo servers (There is one right now running on MRc servers all September long, you may give it a try).

As michal 1279 says and the demo version has a lot of 3 cars, a track with different paths, in my opinion it is already a lot for a demo game and of course if you want more tracks and cars you buy the s3 license, that would be my opinion

KY oval is added to the free content and in 6 months LFS the demo servers are full again every afternoon and many of this new users would buy content. win/win