The download is sloooooooow for me! 2+kb/s on my 30MBit line! Are there any alternative links, or torrent links perhaps?

Now this sounds a lot less like a demo and a lot more like a free-to-play version of Rise of Flight. Makes sense given the business model of selling players the ability to fly additional planes (and now field mods on top of that).

If upgrading to the full ICE package (or even more) remains a cinch, then it ought to bring a lot of new players into the community.

do the demo still need to connect to the internet for playing?
is it possible to play offline?

I'm no expert so could be wrong, but I think you have to register an account online, and then start up the demo and sign-in. Once you've done that once then you can play offline. It's more of an entire 'free-to-play' game than a demo nowadays, with the extra aircraft and field-kits being how they make money.