I've been running Debian on my X1 gen 3 since the day I got it. The only problem was Debian doesn't ship with drivers for proprietary NICs and you have to supply them separately, but that's a Debian problem, not an X1 problem.
I'm currently typing this while USB-tethered through a stock Android phone, which 'just worked' when I first tried it - the only settings screen I've ever seen when USB tethering is the one that toggles it on.
It is normal for linux to perhaps have a driver issue with a very new laptop, but it's usually sorted out in a month or two, especially with thinkpads as they have a large linux-using population.
I'm currently typing this while USB-tethered through a stock Android phone, which 'just worked' when I first tried it - the only settings screen I've ever seen when USB tethering is the one that toggles it on.
It is normal for linux to perhaps have a driver issue with a very new laptop, but it's usually sorted out in a month or two, especially with thinkpads as they have a large linux-using population.