What is your suggestion?: Remove ToB ornament kits from the purple chest drop table and add them to a tertiary drop table, similarly to the Twisted horn/Twisted kits from CoX.
Is this in OSRS?: Yes, the ToB ornament kits are received as tertiary drops like the Lil Zik pet and Metamorphic dust in OSRS. At least that is how OSRS Wiki states it.
Has this suggestion been accepted already?: No, I don't think so.
How would this benefit Alora?: It would make it similar to OSRS and it wouldn't mess with the rarity of getting the other drops, though I am not sure how does it calculate which drop you actually get as the rates are not announced as of yet I believe. In my opinion, it does not make any sense to have them in the same table as other uniques received in purple chests such as the Avernic hilt and Scythe of Vitur because they are special drops only received from the HM and are purely cosmetic.
In the current way more people might do more HM ToB overall and boost the activity but most people are looking for the better rate of the "actual uniques" anyway when doing the HM version. At this moment, they seem more rare than they are in OSRS and this is an RSPS after all. I would say a flat 1/100 chance to roll on the ornament kit table or something would be logical IMO. Not sure about the OSRS rates for these kits. I don't think they are announced as of yet so there is room to experiment.