Further discussion on my RS thread now. This one by 'Uncle Pob' was interesting, and does make sense to me, which could indicate either that the change (if Mod Stu is right that it is no longer f2p) is likely to be either a bug or a mistake:
"Seems like a strange thing to alter.
Jagex can obviously decide, on a whim, to make F2P things members only and vice-versa - but when they do, the whole feature is affected rather than a singular aspect unless there are logical reasons for it: magic logs being F2P doesn't mean magic trees are, purely because there are still no magic trees in the F2P area - that kind of thing.
So if the cremation drop has become members-only, it will be because Jagex may have decided to make the cremation ability itself a members-only ability. So in addition to the drop being removed from the drop tables, any F2P who gained the ability in the past should find that attempting to burn bones should produce a message that you need to be on a members server to do that - because abilities and buffs gainable only through membership cannot be used at all on F2P servers, including by F2P accounts that used to be members.
So are you blocked from burning bones now? I can't find this out, so I don't know.
If you can still burn bones, then there's a bug somewhere: either Jagex intended to remove the ability, but forgot to flag the cremation ability itself as members-only, or the removal of the drop was itself an error. That is, of course, assuming the drop has been removed and not simply been made very very rare."
It might be an idea for those of us who have been killing say more than 3k ghosts (since Mod Stu's reddit post indicates it was a 1/1000 chance drop) to try to get cremation, to make an ingame 'bug' report, and see if anything comes of that. If you do, mention in the report that other f2p players have previously got cremation from ghost kills, and roughly how many ghosts you have killed yourself and still been unsuccessful.