It seems odd nobody at TI pointed out the Circus Train being built before it left the station. The successor PEB and Firehose made a huge and unwieldy combo itself.
Then again, compared to the TI-990 system, maybe they thought they were "thinking small."
But I guess you could take the skyscraper approach some of the ZX81/Timex expansions chose. Or just keep sticking additions off the Back Porch. Some companies just sold boards and let the user figure out what to do with 'em. Don't forget the "real" keyboard upgrades