To be clear it would still be possible to control witnesses by spliting stake, but it would be much more difficult.

As I've said for a looooong time. If it can happen, it will happen. DPOS is a flawed equation. Stake size is everything.

It can never be decentralized properly as it would necessitate people giving up power voluntarily to others, - and that never happens (except as an 'appearance exercise' - ie.e nepotism).Look at the steem train wreck right now.
After 4 years or so, we can see that it's not really happening.

The steem / hive split is proof of the 'might is right' ethos in DPOS.
That is not decentralized.(nor will ever be).

Imagine if Jeff bezos decided to take over steem or hive with stake? Nothing to stop him.
Imagine if the same bezo's decides to just down vote all posts and not post himself. There is nothing to stop him nullifying all upvotes.
(think bloom account with me, but on steroids).

IF the DPOS system was to take off, and serious money got involved - what do you think would be result?
A distribution mechanism that rewarded merit, or continuing nepotism and circle voting to take the inflation 'rewards' for themselves?

It has nothing to do with coding, but ethical codes, embedded in the coding - which can be done).
The problem with this is,of course, is that it would still take the witnesses to agree...aaaaaand we're back to DPOS, flawed equations, and people not giving up their power...

You can put lipstick on a pig, but....