Merc have already wrapped up the WCC and LH should wrap up the WDC in Turkey, leaving 3 more rounds (2 in Bahrain and the last round in Abu Dhabi) so all they have left to race for this season is padding their stats ... so how cool would it be if the did something more exciting and LH and GR swapped seats for the last 3 rounds?!
We could get to see what GR is made of, and all the newer fans who say "how would Lewis do in a bad car" would finally get an answer. .. so no question it would fun for all the fans.... It would also be good for the drivers. GR could finally score a point and get the monkey off his back and LH could have a mental break from the pressure of trying to win every single race.
The teams should also benefit - I back LH to score the illusive 2020 point in the Williams more than I do GR. And Merc could evaluate GR in a competitive setting - with maybe even have a mini shootout with VB ... and VB could be evaluated as lead driver for 3 races to see if he could do the job if (god forbid) LH decides to pull a Rosberg at the end of 2020 - or if he leaves at the end of 2021.
The only downside would be for Alfa Romeo if LH managed to score more points in the last 3 races than their two drivers managed to score over the whole season ... or am I just being a fanboy?