Apart from currency...
Currency is irrelevant these days as anyone will have to go through all the sims and approvals regardless of when they last flew a 737. Sure it might be easier for someone who is current but if you were a 737 check captain for 20 years but now flew something else I don't think a transition back to a 737 would be that difficult. By requiring currency they are limiting the pool of candidates significantly. Unless of course this is for show and the candidate has already been selected.