I personally never liked the gambling aspect of the game. People get addicted and frustrated, that's also the cause for all this toxicity. It's not healthy for the players nor the game.
Clearly the 1M limit hasn't worked due to the number of middleman scams, unfortunately the stakers haven't figured out that we don't actually want them staking, atleast I don't. I wouldn't mind removing the limit, but other changes should be applied.
I'll just throw some random thoughts and ideas about the problems etc.
First it's the accessibility: compared to Scape a majority of players are affiliated to the arena, which wasn't the case previously. The sad part is that even new members are dragged there with the delusion of getting fast cash.
The easiest solution for this is a total level requirement. This also limits the throwaway staking accounts in game, since most of them don't bother levelling at all. Atleast this way they would actually have to contribute to the game at some point. Membership requirement could also be a thing.
This will be really controversial though, since these people don't care about skilling or levelling. We could potentially lose players, I'm not sure if Thomy is willing to take the risk.
Cash only stakes: this is actually something I really like. It has made the job much easier for staff members (I won't get into detail on this one, but reverting would be plainly stupid). Also it has given us stable prices. They might be low, but atleast they're stable.
If it was to be removed, yes there's a possibility that some of the items skyrocket, but we don't really have such collector-like stakers right now. Let's say it does happen though, it wouldn't take long until that person is cleaned and the items are dumped again. We've been there, huge price crashes, really unstable and fluctuating prices. The gamble isn't worth it.
Also you're forgetting the fact about how overflowed we are with items, cash is not the problem. We need item sinks for that, not some potential stakers who might be interested in buying in bulk if the limit is removed.
If cash overflow gets problematic, we just apply a temporary staking tax. Since most of the cash is moving around that it would be the most effective sink. Considering how popular the place is, it doesn't even have to be a high tax. But as I said, since item overflow is far worse than cash overflow, we have to deal with the items, not the cash.
As far as the toxicity is concerned, harsher and more effective punishments will do. Also restrictions (total level, membership) will reduce the number of accounts people can stake with, so it will improve. Temporary staking restrictions (+mute/ban) could also be a thing.
TLDR: remove 1M limit, don't enable item stakes, item sinks (to improve economy), add temporary staking tax if cash is overflowing, harsher punishments for toxicity.
In my opinion the optimal yet risky solution would be a complete removal of arena (even non-stake duelling). Focus will shift to pking. Scams would take place at first, but hopefully stakers have enough wit to stop.
Risk would come from stakers quitting entirely.