I think McConnell has played a blinder politically. The GOP can get rid of him for good without having to do anything themselves and can then blame it all on the Democrats.
Delaying the impeachment trial until after Jan 20th will mean the Dems will need 17 Republicans on side to convict Trump but they wont need any Republican votes to ban him running again as they just need a simple majority for that. Problem with that is it will be seen as party politics. Some of the Republicans who would have voted to ban him running again won't need to because they know the Dems will have enough votes on their own. Therefore they can have their cake and eat it by keeping their base on side.