It should go just like the oX acquisition. Ran parallel for a while then pluck the best and consolidate. Running side by side would be too expensive. They never lit up the oX API and I would have some doubts that it survives.
TDA's client was identical to TOS as the Schwab merger came about. TDA had stopped the TDA client revisions and had been pushing the TOS client all along. Schwab isn't going to throw away all the goodwill associated with TOS. At least I hope not as 20% of my LNW is tied up in TDA.
https://www.sec.gov/Archives/edgar/data/316709/000119312520134809/d893414d424b3.htm#rom893414_19 For what it worth the filing was just submitted - few specifics.
I talked to charles schwab sales agent, (since Ameritrade doesn't open account in many countries) and he told me by end of 3rd quarter merging is expected to become fully completed.
Fully completed has nothing to do with integrating the platforms, which will take years. Until than Ameritrade customers will trade like they always have.
Schwab Street Smart does not run on Linux. TOS is written in Java so it does. I hope Schwab offers TOS soon.
I think the ones you mentioned are superior but difficult to use hence the difficulty makes it hard to find the superiority