Will the default's trigger area match the custom's trigger area? Have authors usually kept the default trigger? Then the custom tile would be eye candy, and using the default sounds natural.
The trigger is defined in the nxmo file. If the trigger only differs slightly from the default ones we could still use the custom trigger area. Yes, this is problematic in the sense that the default now has a slightly different trigger in this set, but this is just a temporal solution anyway until the real sprite is finished.
I just looked into this, and it seems that the majority of them have trigger areas that deviate from the standard ones - some only slightly, some to such an extent that the trigger areas wouldn't even overlap. This does throw a bit of a wrench into these ideas, although there might still be a way to do it (automated) with some secondary animation* trickery...
* or rather, with abusing a feature that's not exclusive to secondaries, but was introduced for the sake of them, namely the offsetting of animation positions
This would still mean that the size of trigger areas would often differ between styles though... so I have to say that ultimately, I'm currently leaning towards "just remove them" again. The substitution either involves creating trigger area confusion or subtly breaking existing levels; removing the objects altogether results in a
very clear and obvious break, and since almost all such objects have "pickup" in their name, the missing piece error will make it pretty clear it's due to this.
The pickup skill object in Arty's silhouette style is an edge case. It completely replicated the default one, except for custom lemming sprites. It's no longer necessary to have a seperate object to achieve this now that pickup skills are rendered based on the active lemming sprites anyway, so V12.7.0 (including RC6, but not earlier RCs) replace it with the default one automatically.