If we were mid table I could see the sense in keeping Shan to the end of the season and then looking for the best manager. With the play-offs so likely it is too much of a gamble to stick with him and what would happen if he somehow got us up?
IMO, you could argue that a mid table position is good grounds to install a new manager with a view to a promotion bid next season.
The fact that we still have a good chance of promotion this year, makes the selection of a new manager more complex, as we don't know what division we'll be in.
As others have said, I'm not sure what a new manager, who doesn't know the players, can bring to the party at this stage of the season.
Looking at James Shan's pre & post match interviews, I don't think he would expect it to be a full time appointment & especially in the EPL.
I'd be disappointed if JS isn't retained in some capacity at the end of this process.
I wouldn't be surprised to see a left field appointment when JS's experienced help is named.