It seems to me that it would be good to have a custom rest time in each exercise settings because for a bench I might want 90 seconds rest between sets but for an ab exercise I might only want 30 seconds.

Also under GYM

+1

The system needs something where you can say you are sick or injured for the day

It could be core, flexibility or warm down, etc., just something you could quickly add on if you are in the mood.