Today's announcement is about our ability to trade all US exchange-listed securities. It's not about listing our own equities. This is what it means to be a National Securities Exchange in the US.

So if you want to trade any US exchange-listed symbol, your broker can do that on LTSE (assuming they are a member)

So I could use LTSE to buy a share of MSFT? But MSFT hasn't agreed to follow any of the LTSE's rules. Why would/should anyone buy MSFT on the LTSE?

Or maybe the point is: there's no point in buying shares with LTSE today, even though you technically can do so, and instead I should wait until there are individual listings and buy those?

(And even then, I don't need to use LTSE, I can just buy their shares on NASDAQ with Etrade like I always do…?)

Correct. There is no need for you to transact on LTSE for the specific use cases you've outlined in this thread. We are open for business so, for the first time, you're able to if you want to.

Exchanges don't hold your shares, so once you have them in a custodian account you can do whatever you want with them, regardless of what exchange you acquired them from.

Every broker has its own internal rules about where to direct its order flow. Some "internalize" the trade and don't send it anywhere. Others get paid to direct the order to a specific market maker, exchange, or dark pool (called PFOF).

Others allow their clients to direct orders using a specific trading strategy. If you have a family office it's very likely this is part of the strategy.

However, ordinary retail investors are sometimes locked out of this system. I don't know Etrade's policy in particular, so I can't say for sure what you would have to do.