There is already a new, low capacity entrance/exit in Turnmill Street.

The entrance you mention will eventually be made more permanent,


I'm not sure where I got this from, but I think this exit is currently
really an emrgency entry/exit that finds temporary double use as a
peaks-only entry/exit; a permanent entry/exit is AIUI somewhere there,
maybe even the same location, but rebuilt, altered, whatever.

--
Nick