Things the next space marines codex should do:

• remove the boundary between primaris/non primaris transports. Everyone can ride in everything and it's stupid that they can't already.
• consolidate datasheets. we don't need 7 different kinds of Captain differentiated only by the kind of metal pants they wear.
• seriously, consolidate datasheets. it's time to start combining non primaris datasheets. if they're the vanishing old breed, make them feel like the throwbacks and veterans they are at this point in the setting timeline.
• stop restricting datasheets to the stuff that is physically on the sprue. look how much fun the horus heresy players have with all the stuff they kitbash or convert! I know you think this is a pro-consumer move but it sucks so damn bad.
• make reivers good. why do they have super angry pistols and knives that can't cut butter? they're melee focused terror troops, let them be terrifying in melee.
• just give everyone better stats & attacks instead of all the mental calculation you need to do with doctrines/shock assault/whatever to arrive to the same conclusion