It's not clear, but here's some knowledgeable speculation:
- All M1 models only have 1 Thunderbolt Controller, thus can only handle 2 Thunderbolt ports on all announced models so far.
- All M1 models only support 1 monitor, but up to 6K.
- No M1 model supports >16GB of RAM or 10GB Ethernet.
All of the above seem like bandwidth limitations to save cost that a future "M1X" or "M2" or "X1" would be extremely likely to fix, and that's where you'll see the bandwidth increase.
- All M1 models only have 1 Thunderbolt Controller, thus can only handle 2 Thunderbolt ports on all announced models so far.
- All M1 models only support 1 monitor, but up to 6K.
- No M1 model supports >16GB of RAM or 10GB Ethernet.
All of the above seem like bandwidth limitations to save cost that a future "M1X" or "M2" or "X1" would be extremely likely to fix, and that's where you'll see the bandwidth increase.