Timestamps are now supported which seems to work. The ALSA (system) time is converted back and forth to Jack time (frames) to allow sequencers to record precise time from the hardware. On playback the Jack frame offsets of each MIDI message are offset by the amount of ALSA time required. If jitter causes erroneous time values (negative times, our of bounds time for Jack) then the value is clamped accordingly.
Port aliases are supported by reading a list of aliases from a file. This allows a name to be given for a port so it shows up in Jack in a meaningful way. Otherwise the ALSA name is used which maybe useless ("USB") and also contains other data like the bus number: "[hw:4,0,1]" which will change if the USB devices are enumerated in a different order. If stuff does change you just have to fix it in the config file and all programs that use the port will just be able to deal with the alias name instead.