To clarify around the release candidate build: You can use the release candidate build, once released, to create your new custom pickup skill objects. You do not have to wait for the stable release before submitting them - you may submit them during the RC phase, to be included with the initial V12.7.0 stable release. If you wait until after the stable release to submit them, they will get included in the December styles update.
Custom pickup skill objects are not officially supported, and a decision has been made not to accept any new ones until official support for them is added, which will be happening in the next major update, V12.7.0, which will release sometime in November.
Existing ones may be updated - and except for two in Plom's styles, I believe all existing custom pickup skill graphics still need to be!
No ifs, ands or buts - if your custom pickup skill object does not already exist in the NL styles download, it will not be added to the NL styles download, full stop. Do not create such objects. If you want to do something with custom pickup skill objects now, update your existing ones. I should be releasing a V12.7.0 Release Candidate build in about a month, at which point you can start preparing for V12.7.0's pickup skill system - and that should end up being the last time you need to update them, as the whole point of it is to make it so you can use custom pickups without having to update them all the time.
Additionally, I find it especially bothering that one author created a whole bunch of new ones - some for entirely new styles, some as the only new piece added to existing styles - yet hasn't done anything to update their existing ones that need it. When you do this with your own level packs, whatever, that's your choice. But when it comes to styles, which other people may be relying on, I think it's a completely fair expectation that if you have time to create new styles, you have time to maintain your existing ones at least to the extent that they don't end up not working and/or giving false information to the player.