thats that billion/trillion dollar question :)
so I think theres a huge design space, and I think it partially turns into a "mechanism design" challenge to articulate a landscape of transaction / market auction mechanisms that
1) incentivize maximizing market liquidity
2) recognize the speed of light is finite, and have that inform the minimal time scale matching can happen on.
3) obviate/remove the need to obscure large trades as a large number of smaller trades (which is half the value of so called algorithmic trading strategies to institutional investors). This could be via having one design constraint on auctions be that the market impact of the sum of the small trades should be equivalent to the single large trade. (ignoring the issue of the exogenous information of there was a large trade ).
some interesting knock on consequences of these ideas are the following
1) the larger the time scale you're willing wait for the trade to be matched to "the other side", the cheaper it should be to trade! (creating liquidity is valuable!)
2) if you're willing to allow your trade to be "partially matched" instead of all or nothing, that too creates liquidity.
the point being, you start with "what are all the complications of how people do large/complicated trades today that should just be trivial with the right auction" is sortah my perspective. thats glossing over a lot of complexity and other concerns, but those are some high notes.
that said,this is just the tip of the iceberg, and these sort of market design questions are genuinely under studied in my mind, and i could easily spend hours talking about this in greater depth over coffee or such.