Detail upgrades for the Kato Maxi-Is & -IVs would be very welcome, to replace the plastic walkways esp. to fit in with more recent releases of other prototypes (feels weird to think of the Kato cars as 'old'!) Traincat/Bob had a set for the Is available & sets for the IVs in final revision before he put the business on hold, which was a while ago now.
I agree with previous suggestions about detail upgrades for Atlas Trainman cars, the Thrall 4750 hopper would be a good choice (also previously offered by Traincat but no longer available)