What cops did for years and years is called transition to sidearm, because the shotgun is now useless...
Aippi I saw that a lot during qualifications and scenario based training too. We used to have monthly stress shoots. Honestly, after we did that for a while and everyone put more rounds through the shotguns, proficiency improved a lot. Then we traded for 11-87's.
Rutgersgrad, I just bough a new 870p this week, model 24407. I would be totally uninterested in an express model. The 870p is far superior. That being said I wish I had the wingmaster I bought in 1968 back again. But if I had it, it would be for limited use, and treated like a prize possession.