I agree with most posters, that they should finish the Tristar first, and then release a couple of service packs for various current aircraft.

After that there could plenty of options with expansion from current basepacks: a RR Convay equipped 707-400, the 707-100, 707-200.. In fact the entire 707 versions up to the -700 series with High bypass turbofan engines.

And then we have the 767-400.

Next in the line, a classic 741/742 would be nice.

Further out in the future we could imagine the DC-8 and Convair 880/990.

BR
Anders