It's contingency planning, Boeing knew that the Max was the last throw of the dice for the 737.
797 had been looked at and rejected as "Grandfathering" the Max was a better option in their opinion (and not without outside influence).
797 will come along a little earlier than planned, how early is up to Boeing.
I would like to think that Boeing will endeavour to make the 797 the best plane they've ever produced.