There are also some unsolved challenges with Multipath TCP, at least last time I studied it in 2014/2015. For example, when multiple good links are available,

There are also some unsolved challenges with Multipath TCP, at least last time I studied it in 2014/2015. For example, when multiple good links are available, Multipath TCP will tend to flip flap between them rather than stabilise on one or the other. You can also get massive reordering which will tend to throw off the congestion control algorithm, but I believe that issue has since been resolved. Good chance are there are some other issues that make MPTCP not quite suitable for widespread use right now.