One of my favorite parts of the UK pavilion was always the quaint little toy shop that had the Mr. Men and Little Miss books. Just one of those nice unique touches that Disney unfortunately doesn't have any more. I believe it is now a shop for UK Bands merch (Beatles, Rolling Stones . . .), which still fits the theme of UK pavillion but lacks that authentic charm.
For the new attraction, I could see a simple Poppins carousel working well. Of course, a Toad ride would be really cool but probably won't happen. In the end, I would rather Disney do something small but appropriate than something larger scale that overly dominates the pavillion.