There were also some server issues happening with the vanity stuff last night - for the first couple of hours I was getting a time out error before the suit customisation menu would even load, but that eventually settled down. I was getting the "changes are a few steps behind" issue that others have mentioned as well, but this could also be server related. At least some of these weirdnesses feel like they'll be taken care of as the server situation settles down.
I think the main reason we can't use our old Flight Suit cosmetics with the new Artemis/Maverick/Dominator suits is because the "clothing slots" have changed. The older cosmetics come in three pieces: torso, sleeves, and trousers. The new suit cosmetics are double that: there's separate shoulder and wrist pieces, and separate belt and knee pad pieces. While I would love to put a pair of blue camo pants over my Maverick suit, or wear one of my glorious orange jackets over my Artemis, that just doesn't jive with the modular system FDev have decided to use moving forward. It isn't just about knee pads potentially clipping through the trousers or elbow pads getting lost in the sleeves either: there's weapons and jump packs and all that goodness as well. Making the existing cosmetics jive with the new system is a headache with a very small payoff. FDev have made the decision to split between old cosmetics and new cosmetics at this stage... and fair enough? That's a sensible use of time and resources, I'm glad they chose to spend that time doing something else rather than facilitating my jackets collection.
That said, I would like to see a little bit of overlap eventually, if that's something FDev are able to tinker with at some point down the line. When you purchase one of the new cosmetic bundles, you can use them with the "wrong suit" - so you can buy one of the new Dominator skins, and wear it as part of your Artemis customisation. It would be nice to see some of our purchased flight suit options added in there (the Explorer Flight Suit would jive with the Artemis really well, imo) as well as the option to wear the Maverick suit as a flight suit skin - letting us (cosmetically, at least) have the look of wearing our jackets and pants over the newer suits.
Eventually getting the option to wear jackets and pants over an actual Maverick suit would be cool too. Teaching the game "if they equip sleeves, unequip any shoulders and wrists stuff" seems like a pain in the ass, but perhaps having a version of the old cosmetics that jives with the new cosmetics system which unlocks for those of us who've purchased already - eventually, when they don't have more pressing/important things to spend their time on - might be nice.